The final NCCE is actually more insidious than it seems at first. What's the rationale for null terminated strings? Monitor the software for any unexpected behavior. This listing shows possible areas for which the given weakness could appear. If all pointers that could have been modified are sanity-checked previous to use, nearly all NULL pointer dereferences can be prevented. So before writing anything to some memory location memory has to allocated to the pointer. It does not give the pointer a new value. 4500 Fifth Avenue <. Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an address inappropriately aligned for the type of object pointed to, and the address of an object after the end of its lifetime. When length is zero, it is probably unusable condition for this function. In your case you are not doing it,so you have a segmentation fault(or crash) . How to remove elements from a generic list while iterating over it? I'd guess WG14 has considered these questions, but I haven't until now :). I'm getting a warning while doing a Static Analysis (SA) on my code. It's not them. {"serverDuration": 277, "requestCorrelationId": "e2a1d936a1543fbd"}, EXP34-C. Do not dereference null pointers, Clever Attack Exploits Fully-Patched Linux Kernel, ERR33-C. Detect and handle standard library errors, one compliant and one non-compliant example, CERT Oracle Secure Coding Standard for Java, EXP01-J. *var1 = 0; this dereferences the pointer, i.e. then the UB is not in your code, you just may be searching for code with potential UB. Not the answer you're looking for? This code also violates ERR33-C. Detect and handle standard library errors. *var1 = 0; this dereferences the pointer, i.e. Without coverity i probably would not have found this copy&paste error. How come an array's address is equal to its value in C? I think that checking for user_data being NULL would be an improvement to the CS so long as there is an explicit mention that user_data being NULL is invalid even if length == 0. Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Correct; a null pointer is not a valid pointer for the C library functions. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. (C11, S7.24.2.1). 0 is certainly within the 'domain of the function' (a phrase defined by mathematics but not by C11), as copying 0 bytes is well-understood (although silly). If code1 and code2 may both be true, though, then you do have a substantial bug here. This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. User without create permission can create a custom object from Managed package using Custom Rest API. Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). repository mruby/mruby prior to 3.2. We didn't figure ourselves where those threading issues came from and tried to hide them with hacks. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. <, [REF-18] Secure Software, Inc.. "The CLASP Application Security Process". Common logic to perform in the middle? ), Does not guess that return values from malloc(), strchr(), etc., can be NULL (The return value from malloc() is NULL only if there is OOMo and the dev might not care to handle that. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Suppressing a null dereference warning in static analysis coming from stub implementations in tests, Visual Studios giving me Dereferencing Null Pointer warning. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". One situation this can happen is when the pointer has been checked against NULL and is dereferenced later. What REALLY happens when you don't free after malloc before program termination? A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things. The format With two string literals, "SGI_ACL_FILE" and "SGI_ACL_DEFAULT", the addition of the (unsigned char *) cast resulted in sizeof returning 7 (size of pointer minus one), rather than the length of Impacts a highly used used area of our code which could cause problems when running for extended time. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Coverity is correctly telling you that, albeit in a somewhat indirect way. return p == NULL || (char *)p < &_etext; Find centralized, trusted content and collaborate around the technologies you use most. OS allows remote attackers to cause a denial of service (crash from null dereference) or execute arbitrary code via a crafted request during authentication protocol selection. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc. with solve of this bug problems have gone. Right? That makes sense. I've changed it to say null pointer instead of invalid pointer. and Gary McGraw. race condition causes a table to be corrupted if a timer activates while it is being modified, leading to resultant NULL dereference; also involves locking. And in this case, there is no pointed-to data. The libpng library allows applications to read, create, and manipulate PNG (Portable Network Graphics) raster image files. FWIW the pointer arithmetic is also invalid because p1 does not point to valid memory, so you scan't just say something like, That code does not violate th is rule, but it violates ARR30-C. Do not form or use out-of-bounds pointers or array subscripts. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. void host_lookup(char *user_supplied_addr){, if("com.example.URLHandler.openURL".equals(intent.getAction())) {. Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? which bolsters my assertion that x->member dereferences x (or at least an offset of x). A common memory-leak idiom, is reallocating storage and assigning its address to a pointer that already points to allocated storage. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The platform does add offsetof( struct_type, member) to input and dereferences that. Note that this code is also vulnerable to a buffer overflow (CWE-119). Possible Null Pointer exception was found in a feature in which I'm the feature owner. I added an assertion to that compliant code example. The test was added to catch the possibly theoretical situation where the length of input_str was somehow the maximum size for size_t, and adding one to this size in the malloc expression (to allocated space for the trailing null byte) results in an integer overflow. but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. If the operand has type "type", the result has type "pointer to type". Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. In this scenario, by the time, I come in 'cond2', I already have 'q' set. It modifies the pointed-to data. What were the most popular text editors for MS-DOS in the 1980s? The issue is: memcpy() and friends do not explicitly state that a null pointer is a valid pointer value, even if the number of bytes to copy is 0. Pointer members in structs are not checked. Solutions I propose: .. In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? Would you like to help any further according to different understanding and expectations for affected implementation details. Clearly the standard enumerates 1 case of undefined behavior, but makes no special mention of n=0. Game allows remote attackers to cause a denial of service (server crash) via a missing argument, which triggers a null pointer dereference. <, [REF-1031] "Null pointer / Null dereferencing". Whoops, you're right. Copy & paste errors might not often cause system crashes, but developer headaches. This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. Specifically, it understands that Equals is meant to test equality, and that you're comparing x to null as if they might be the same (the "check"), but you can't get into Equals (the "path") at all because of the NullReferenceException. Where does the version of Hamapil that is different from the Gemara come from? Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Coverity - Explicit null dereferenced (FORWARD_NULL) in contentResolver.delete(), Coverity report meanings - PW.INCLUDE_RECURSION, Extracting coverity .csv file from coverity server, C# Coverity giving "Dereference before null check (REVERSE_INULL)" on a RemoveAll call to remove null entries from a list. In that case, if you want to change the value of the pointed-to data, well, have the pointer point to some writeable memory first! This information is often useful in understanding where a weakness fits within the context of external information sources. The sk pointer is initialized to tun->sk before checking if tun is a null pointer. Negative index used in the code could result in a totally wrong behavior in the application. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? mruby is vulnerable to NULL Pointer Dereference Affected Software. This defect on our template caused null pointer deferencing in over hundred use cases. Because null pointer dereferencing is undefined behavior, the compiler (GCC in this case) can optimize away the if (!tun) check because it is performed after tun->sk is accessed, implying that tun is non-null. Using platform-specific means (e.g. Because null pointer dereferencing is undefined behavior, the compiler (GCC in this case) can optimize away the if (!tun) check because it is performed after tun->sk is accessed, implying that tun is non-null. May be you need to do this null check much before. Apple. Are these quarters notes or just eighth notes? Should I re-do this cinched PEX connection? I suppose there is a question of "Is a pointer that points to 0 bytes valid?" We should Zoom if you wish to talk more. CWE is sponsored by the U.S. Department of Homeland Security (DHS) Cybersecurity and Infrastructure Security Agency (CISA) and managed by the Homeland Security Systems Engineering and Development Institute (HSSEDI) which is operated by The MITRE Corporation (MITRE). Coverity is giving you a warning because you are in fact doing a NULL check: Here, a_ptr is evaluated in a boolean context. I got the impression that 31 source files of Linux modules will need further adjustments. While not explicitly mentioning UB, I would infer that *NULL is UB since NULL is not a pointer to an object or function type. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. It also permits &x[y] to translate to x + y, but that is still UB if x is null because of ARR38-C. ISO C just has no similar wording for x->member. A boy can regenerate, so demons eat him for years. Yes -> horrible false positive No -> You removed an important piece of information. This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer. One of the Coccinelle software maintainers expressed opposite development views today. Fixed by setting name to Oh joy. What should I follow, if two altimeters show different altitudes? What are the arguments for/against anonymous authorship of the Gospels, Two MacBook Pro with same model number (A1286) but different year, Simple deform modifier is deforming my object. For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). Why are players required to record the moves in World Championship Classical games? If the compiler finds a pointer dereference, it treats that pointer as nonnull. SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. Is it safe to publish research papers in cooperation with Russian academics? The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? <, [REF-1033] "NULL Pointer Dereference [CWE-476]". Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. May it be expected that the address of operator will eventually be evaluated only after a pointer dereference for a desirable access to a data structure member? Category. Phew, we're agreed here. What does 'They're at four. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact. Possible Null Pointer exception was found in a feature in which I'm the feature owner. More specific than a Base weakness. Connect and share knowledge within a single location that is structured and easy to search. Category - a CWE entry that contains a set of other entries that share a common characteristic. What is it that I did not understand? (where the weakness is a quality issue that might indirectly make it easier to introduce security-relevant weaknesses or make them more difficult to detect). CalebFenton/simplify. Asking for help, clarification, or responding to other answers. Asking for help, clarification, or responding to other answers. I'm learning and will appreciate any help. But no where in that particular idiom would a NULL pointer necessarily be deferenced. One could argue that all code examples would be redundant with the first pair. Even if that memory contains a pointer which is not valid, or has been freed. As a result, this noncompliant code example is vulnerable to a null pointer dereference exploit, because null pointer dereferencing can be permitted on several platforms, for example, by using mmap(2) with the MAP_FIXED flag on Linux and Mac OS X, or by using the shmat() POSIX function with the SHM_RND flag [Liu 2009]. Setting an incorrect jump target leads to a certain crash if the code is exercised. I'll just provide a few references to back up my beliefs. It was causing glusterd daemon crash for glusterfs. If malloc() fails, it returns a null pointer that is assigned to c_str. Why don't we use the 7805 for car phone chargers? This code will definitely crash due to a null pointer dereference in certain cases. Making statements based on opinion; back them up with references or personal experience. The idea is not to guarantee validity, but to catch a substantial number of problems that could occur. This rule applies to all null pointers, regardless of which function returned them. Various developers and code reviewers are struggling also with evolution of the specifications for such programming languages. The chunkdata pointer is later used as a destination argument in a call to memcpy(), resulting in user-defined data overwriting memory starting at address 0. If the operand is the result of a unary * operator, neither that operator nor the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. Shouldn't the function check all pointers before dereferencing them or passing them to another function? I would, at the very least, put an assert(q) inside if (code2), but: Ideally you'd stick with that one if/else and put all your logic in there. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. }. The code processes a physics modification option line given either from the command line or file. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. This compliant solution ensures that both input_str andthe pointer returned by malloc() are not null: This noncompliant code example is from a version of drivers/net/tun.c and affects Linux kernel 2.6.30 [Goodin 2009]: The sk pointer is initialized to tun->sk before checking if tun is a null pointer. If you want to change the value of your pointer, just do. Improper Check for Unusual or Exceptional Conditions, Unchecked Return Value to NULL Pointer Dereference, Memory Allocation with Excessive Size Value, Improperly Controlled Sequential Memory Allocation, OWASP Top Ten 2004 Category A9 - Denial of Service, CERT C Secure Coding Standard (2008) Chapter 4 - Expressions (EXP), CERT C Secure Coding Standard (2008) Chapter 9 - Memory Management (MEM), CERT C++ Secure Coding Section 03 - Expressions (EXP), CERT C++ Secure Coding Section 08 - Memory Management (MEM), SFP Secondary Cluster: Faulty Pointer Use, SEI CERT Oracle Secure Coding Standard for Java - Guidelines 02. There are other problems with this code, as is noted in the rule. While there are no complete fixes aside from conscientious programming, the following steps will go a long way to ensure that NULL pointer dereferences do not occur. However there is no portable way to verify that the pointer is valid, other than checking for null. uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); can have the value zero on a call to that function. This is not a perfect solution, since 100% accuracy and coverage are not feasible. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Not sure if this is directly related to the error/warning you get but in general I think you should rather use, C# Coverity giving "Dereference before null check (REVERSE_INULL)" on a RemoveAll call to remove null entries from a list, How a top-ranked engineering school reimagined CS curriculum (Ep. Which language's style guidelines should be used when writing code that is supposed to be called from another language? Asking for help, clarification, or responding to other answers. The occurrence of this wrong index was not seen in the code. If your code examples are simply searching for instances of C code of this nature, then the UB is not in your code, you just may be searching for code with potential UB. A Community-Developed List of Software & Hardware Weakness Types, Technical Impact: DoS: Crash, Exit, or Restart, Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory. How to force Unity Editor/TestRunner to run at full speed when in background? Thanks for contributing an answer to Stack Overflow! Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. This compliant solution eliminates the null pointer deference by initializing sk to tun->sk following the null pointer check. FORWARD_NULL. The two languages try to maximize compatibility, . Software Engineering Institute Why don't we use the 7805 for car phone chargers? Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. In the following code, the programmer assumes that the system always has a property named "cmd" defined. What's the cheapest way to buy out a sibling's share of our parents house if I have no cash and want to pay less than the appraised value? Is there a generic term for these trajectories? Variant - a weakness First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. NULL can't point to data. Finding the distance from a corner of a cube to the midpoint of an edge. Which language's style guidelines should be used when writing code that is supposed to be called from another language? Yes the ordering matters. how to remove a project from coverity-scan, Remove duplicate results from multiple Coverity runs, Coverity. If a user supplies a malformed request or violates the client policy, the Do method can return a nil response and a non-nil err. He also rips off an arm to use as a sword, Canadian of Polish descent travel to Poland with Canadian passport, assertions usually only apply at debug-time (as I was recently reminded with a runtime crash in a release build that made no sense after all, I have assertion safety everywhere, right?). rev2023.5.1.43405. Believing that dereferencing NULL shouldn't crash the system doesn't make it true. Coverity Collector User Votes: 0 Vote for this issue Watchers: 1 Start watching this issue. Asking for help, clarification, or responding to other answers. You have defined pointers var1 and var2 of type uint64_t and char respectively which are pointing to NULL . Find centralized, trusted content and collaborate around the technologies you use most. The indicated severity is for this more severe case; on platforms where it is not possible to exploit a null pointer dereference to execute arbitrary code, the actual severity is low. Network monitor allows remote attackers to cause a denial of service (crash) or execute arbitrary code via malformed packets that cause a NULL pointer dereference. */. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. How to force Unity Editor/TestRunner to run at full speed when in background? I reordered that code example to do all the checks before allocations. The question is concise, clear, to-the-point and logical. Aaron:I suspect we are talking past each other. 0->member is undefined behavior. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Note that it doesn't know how to check for non-heap, non-stack. See C17 7.1.4p1, which says, in part: Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow: If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointerto non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after default argument promotion) not expected by a function with a variable number of arguments, the behavior is undefined. In Coverity, FORWARD_NULL reports defects when there are enough evidences to be sure the null access will (can) happen. In your code example, the p1my_item will be evaluated before t he & operator, and so this rule is violated, although you are really trying to do pointer arithmetic rather than see what the pointer points to. The purpose of that line of code is to read through the current values in the list and strip out any that have become null, there's no null check happening as far as I can tell. Improve INSERT-per-second performance of SQLite. NIST Workshop on Software Security Assurance Tools Techniques and Metrics. Could I capture, and I would be able to glean much security information from the dump? VM {} is NOT a viable candidate for solving affinity group violation situation. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Configure coverity to check that a declared variable is initialized before usage as a pointer. * @param vmToHost vm to host assignments If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. It's even called out explicitly in C17 7.24.1p2: Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Finally, there is the matter of the compliant solution. Coverity scan helps our developers finding issues like these. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Likewise, pointers to freed memory are not valid. Markus:AFAICT the respponses to this StackOverflow question agree with my previous assertions. This one alone We had some spurious hangs and never knew why. WG21 (the C++ working group) may wish to define 0->y, and they are within their right to do so. Chat client allows remote attackers to cause a denial of service (crash) via a passive DCC request with an invalid ID number, which causes a null dereference. Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. It would have been terrible to A simple decrement that wraps around causing an array overflow on lsm->lsm_oinfo[i[. Allocated memory leaked in several cases. If input is null, that is technically not a null dereference. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. I guess you could write a proposal to modify the C Standard, but our coding standard is meant to provide guidance for the existing language. Do not use a null in a case where an object is required, https://gcc.gnu.org/gcc-4.9/porting_to.html, ARR30-C. Do not form or use out-of-bounds pointers or array subscripts, Reconsidering pointer dereferences before null pointer checks (with SmPL), understand the source code search pattern, One of the Coccinelle software maintainers expressed opposite development views today, https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be, Prior to 2018-01-12: CERT: Unspecified Relationship, Pointer Casting and Pointer Type Changes [HFC], Dereferencing an out-of-domain pointer [nullref], Section 5.2.18, "Null-Pointer Dereference", Dereferencing null pointers that were not returned by a function.
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