This one is pretty awesome. availability of the system. extern char _etext; 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. Expressions (EXP), Weaknesses in the 2019 CWE Top 25 Most Dangerous Software Errors, Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses, Weaknesses in the 2020 CWE Top 25 Most Dangerous Software Weaknesses, Weaknesses in the 2022 CWE Top 25 Most Dangerous Software Weaknesses, Comprehensive Categorization: Poor Coding Practices, https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf, https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf, https://en.wikipedia.org/wiki/Null_pointer#Null_dereferencing, https://developer.apple.com/documentation/xcode/null-reference-creation-and-null-pointer-dereference, https://www.immuniweb.com/vulnerability/null-pointer-dereference.html, Cybersecurity and Infrastructure Security Agency, Homeland Security Systems Engineering and Development Institute, Null Dereference (Null Pointer Dereference), updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities, updated Common_Consequences, Demonstrative_Examples, Other_Notes, Potential_Mitigations, Weakness_Ordinalities, updated Potential_Mitigations, Relationships, updated Demonstrative_Examples, Description, Detection_Factors, Potential_Mitigations, updated Demonstrative_Examples, Observed_Examples, Relationships, updated Related_Attack_Patterns, Relationships, updated Observed_Examples, Related_Attack_Patterns, Relationships, updated Relationships, Taxonomy_Mappings, White_Box_Definitions, updated Demonstrative_Examples, Observed_Examples, updated Alternate_Terms, Applicable_Platforms, Observed_Examples, updated Demonstrative_Examples, Detection_Factors, References, Relationships. IMHO, the rule title should be changed to something less general. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. Category - a CWE entry that contains a set of other entries that share a common characteristic. Apple. Synopsys, Inc. | Policy Statement | Contact, // Create a set of all VMs in affinity groups, // There is no need to migrate when no collision was detected. This means one of two things: In this particular case, you're explicitly setting a_ptr to the address of a variable, so it can't possibly be NULL at that point. FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. As a result, the optimizer may remove null . Believing that dereferencing NULL shouldn't crash the system doesn't make it true. ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. This turned out to be a security flaw, now known as CVE-2015-3237. At best ISO C is under-specified in this regard, and perhaps should explicitly say so. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. In the case of the ARM and XScale architectures, the 0x0 address is mapped in memory and serves as the exception vector table; consequently, dereferencing 0x0 did not cause an abnormal program termination. It is pretty easy to miss such things when adding a new feature. Finding the distance from a corner of a cube to the midpoint of an edge. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. I've posted an example for the sake of completion-. <<< CID 102061: Null pointer dereferences REVERSE_INULL <<< Null-checking " doc_bv " suggests that it may be null, but it has already been dereferenced on all paths leading to the check. It would be tricky, and they would want WG14 (C working group) to at least bless this change, and more likely, make the analogous change to the C standard. I got the impression that 31 source files of Linux modules will need further adjustments. In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution. Why refined oil is cheaper than cold press oil? WG21 (the C++ working group) may wish to define 0->y, and they are within their right to do so. Can corresponding author withdraw a paper after it has accepted without permission/acceptance of first author. New feature implementation got stuck for days because old code had obscure implementation which caused debuging nightmare. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The libpng library implements its own wrapper to malloc() that returns a null pointer on error or on being passed a 0-byte-length argument. Even if that memory contains a pointer which is not valid, or has been freed. This listing shows possible areas for which the given weakness could appear. This information is often useful in understanding where a weakness fits within the context of external information sources. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. Yes -> horrible false positive No -> You removed an important piece of information. The null pointer check for writing or dereferencing should be a compiler flag or library setting. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. "Signpost" puzzle from Tatham's collection, Image of minimal degree representation of quasisimple group unique up to conjugacy. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. For users who are interested in more notional aspects of a weakness. Now it seems that I can inform also Linux contributors with higher confidence about further change possibilities (which I detected by the means of the Coccinelle software again recently). Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. If the operand has type "type", the result has type "pointer to type". Find centralized, trusted content and collaborate around the technologies you use most. But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. of making the mruby interpreter crash, thus affecting the. In the following code, the programmer assumes that the system always has a property named "cmd" defined. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Variant - a weakness One could argue that all code examples would be redundant with the first pair. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. Carnegie Mellon University
NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. . . Thanks! This is a matter of style, and also following code walkthrough. I added an assertion to that compliant code example. The value 0 for the number of bytes to copy is not what causes the UB, it's the null pointer value which triggers it. Not the answer you're looking for? Why are players required to record the moves in World Championship Classical games? Is there any known 80-bit collision attack? I would never have thought of looking at this piece of code if coverity hadn't found it. Each call of the impacted function may consumes many bytes (it's a file path). 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. Which language's style guidelines should be used when writing code that is supposed to be called from another language? patch id. One of the Coccinelle software maintainers expressed opposite development views today. Hence the error. Thanks for this checker. Coverity Prevent cannot discover all violations of this rule, so further verification is necessary, Detects when NULL is dereferenced (Array of pointers is not checked. The different Modes of Introduction provide information about how and when this weakness may be introduced. (In contrast, the case of passing 0 bytes to malloc is addressed in C11.) 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. 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. This pointer was the resaon of a memory leak Realy nice catch by Coverity. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. I'll just provide a few references to back up my beliefs. Can this be fixed if I reassign the *var1 to NULL again ?? If it wasn't for coverity Resource leaks: I hate them, especially in libc, which is code you expect to be hot. Our code base contains a lot of copy paste mistakes, we are glad that there is a tool like coverity that can help to detect them. 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. In my experience, there are reasons to check for a NULL pointer other than dereferencing it. It looks like a logic bug, which can cause a memory leaking. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). 2005. 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. Made code more compliant with other rules. 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. At one point later, I get another warning: It seems like the line a_ptr->ptr = NULL is deemed incorrect/dangerous. This has been there for decade, and was shipped in a real product. The question is concise, clear, to-the-point and logical. .. Would it be ok if I write !cond1 just like this: Logically, based on what you've said, and assuming that code1 and code2 are mutually exclusive, this is a false positive. FORWARD_NULL. Created: Jan 26 2021 02:47:29 PM UTC Updated: Jan 26 2021 10:07:21 PM UTC . This Android application has registered to handle a URL when sent an intent: The application assumes the URL will always be included in the intent. rev2023.5.1.43405. 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. return p == NULL || (char *)p < &_etext; Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator. Then we hit memcpy with length 0. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Using LINQ to remove elements from a List. ), [REF-6] Katrina Tsipenyuk, Brian Chess By 'valid pointers' I mean that both src and dest pointers are not null and they both point to non-overlapping arrays containing at least n bytes each. Image of minimal degree representation of quasisimple group unique up to conjugacy. Assign an array of Swift strings to a C structure variable taking a char ** value. Can I use an 11 watt LED bulb in a lamp rated for 8.6 watts maximum? Find centralized, trusted content and collaborate around the technologies you use most. In some situations, however, dereferencing a null pointer can lead to the execution of arbitrary code [Jack 2007,van Sprundel 2006]. NIST. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. For users who want to customize what details are displayed. can have the value zero on a call to that function. Pointer members in structs are not checked. Negative index used in the code could result in a totally wrong behavior in the application. A non-null but invalid pointer passed to memcpy() can indeed cause undefined behavior, but that is not the issue in the noncompliant codethe pointer will either be valid or null. :). Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. One situation this can happen is when the pointer has been checked against NULL and is dereferenced later. Shouldn't the function check all pointers before dereferencing them or passing them to another function? I say "theoretical" because I have not successfully produced strings of this length in testing. to 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. Asking for help, clarification, or responding to other answers. * Select VMs from the broken affinity group that are running on the same host. Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? Thanks for contributing an answer to Stack Overflow! Unfortunately the problem is much more complex, and generally unsolvable within standard C. Consider the following example: There's no way f can check whether x points into valid memory or not. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. Will the ordering matter a bit more for the safe evaluation of involved expressions? Dereferencing a pointer that might be null " findVmViolatingPositiveAg(affinityGroup, vmToHost) " when calling " getVmsByIds . 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]. Coverity complains below message: CID 25469 (#1 of 1): Explicit null dereferenced (FORWARD_NULL) 9. var_deref_op: Dereferencing null pointer q. I do not understand why coverity complains here. Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? It should be an ingrained practice. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. It worked normally, but sometimes devices had cryptic types. This noncompliant code example is derived from a real-world example taken from a vulnerable version of the libpng library as deployed on a popular ARM-based cell phone [Jack 2007]. Why is this error being shown and is there a way to correct it? Thanks for the reference to Julia Lawall's response to your question. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. 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. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself. }. This is the intention for the referenced small script of the semantic patch language. 0->member is undefined behavior. 2019-07-15. It would cause game actors to teleport to the wrong coordinates. very useful to find this very horrible bug in this case, we're using a pointer to memory which is not guaranteed to be zero, and potentially corrupting the malloc arena in the process. Example: tool developers, security researchers, pen-testers, incident response analysts. If input is null, that is technically not a null dereference, but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. Chains can involve more than two weaknesses, and in some cases, they might have a tree-like structure. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. More specific than a Pillar Weakness, but more general than a Base Weakness. 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. ), NPD.CHECK.CALL.MIGHTNPD.CHECK.CALL.MUSTNPD.CHECK.MIGHTNPD.CHECK.MUSTNPD.CONST.CALLNPD.CONST.DEREFNPD.FUNC.CALL.MIGHTNPD.FUNC.CALL.MUSTNPD.FUNC.MIGHTNPD.FUNC.MUSTNPD.GEN.CALL.MIGHTNPD.GEN.CALL.MUSTNPD.GEN.MIGHTNPD.GEN.MUSTRNPD.CALLRNPD.DEREF, 45 D, 123 D, 128 D, 129 D, 130 D, 131 D, 652 S, Checks for use of null pointers (rule partially covered). However, the warning has value because it is pointing [sic] out that the safety of q is not trivially obvious from your function's logic. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Clearly the standard enumerates 1 case of undefined behavior, but makes no special mention of n=0. Unexpected behavior can be pain to hunt down when one of these is involved. then the UB is not in your code, you just may be searching for code with potential UB. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). Checker. This code also violates ERR33-C. Detect and handle standard library errors. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". Do you find another previous clarification approach interesting and helpful? 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? Thanks, David! it may still not be enough to satisfy Coverity. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. To learn more, see our tips on writing great answers. Monitor the software for any unexpected behavior. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. ', referring to the nuclear power plant in Ignalina, mean? Why does the second compliant example permit using possibly-null pointers? It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). I doubt that "length" of zero is a valid parameter, and although there no copy, but we see memory allocation. you are trying to make your var1 to point to the same location as that of var2 and casting it to uint64_t.So from the above two sections var1 and var2 are pointing to NULL pointer ie nothing in simple terms. 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. I reordered that code example to do all the checks before allocations. Episode about a group who book passage on a space ship controlled by an AI, who turns out to be a human who can't leave his ship? This fixed weird behaviour that was really hard to find. To learn more, see our tips on writing great answers. This vulnerability is capable. We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. 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. Thank you for the description (comments).It Cleared my doubts. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Asside - I would suggest initialising your pointers to, It's impossible to tell from that code whether. that is linked to a certain type of product, typically involving a specific language or technology. First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. ROSE does not handle cases where an allocation is assigned to an lvalue that is not a variable (such as a struct member or C++ function call returning a reference), Finds instances where a pointer is checked against NULL and then later dereferenced, Identifies functions that can return a null pointer but are not checked, Identifies code that dereferences a pointer and then checks the pointer against NULL, Can find the instances where NULL is explicitly dereferenced or a pointer is checked againstNULL but then dereferenced anyway. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 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. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); This table specifies different individual consequences associated with the weakness. 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! No affinity group collision detected for cluster {}. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? */. We should Zoom if you wish to talk more. Running through Coverity reports and it is having issues with the "onsSelectedCredentials.RemoveAll(x => x.Equals(null));" line here, stating "check_after_deref: Null-checking x suggests that it may be null, but it has already been dereferenced on all paths leading to the check." SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. Separate it into a different function that you can call. Simple deform modifier is deforming my object, xcolor: How to get the complementary color. At this point we define size as strlen(input_str) + 1. Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. The added benefit of this is that you probably no longer require both p and q and so the entire function becomes far more lean. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. Dereferencing a null pointer always results in undefined behavior and can cause crashes. 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. It depends on the specific details, but in general, taking the address of any valid memory is OK. We didn't figure ourselves where those threading issues came from and tried to hide them with hacks. Generating points along line with specifying the origin of point generation in QGIS. Standing by. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. The correct idiom is to only allocate storage if the pointer is currently NULL. 4500 Fifth Avenue
that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. It's not them. It would have been terrible to A simple decrement that wraps around causing an array overflow on lsm->lsm_oinfo[i[. So no checking of the length is necessary (besides preventing integer overflow, which the compliant solution does). Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. Canadian of Polish descent travel to Poland with Canadian passport. What is it that I did not understand? Example: educators, technical writers, and project/program managers. In this scenario, by the time, I come in 'cond2', I already have 'q' set. If input is null, that is technically not a null dereference. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. The description The sk pointer is initialized to tun->sk before checking if tun is a null pointer. is provided for a non-compliant code example.Thus it seems that the arrow operator (member access through pointer) is usually treated also as a dereference operation. Should I re-do this cinched PEX connection? An extremely nice thing which was discovered only by Coverity. Extended Description NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Thank you for clarifying your assertion until I understood it properly. NULL can't point to data. Coverity scan helps our developers finding issues like these. Note that it doesn't know how to check for non-heap, non-stack. The choice could be made to use a language that is not susceptible to these issues. Connect and share knowledge within a single location that is structured and easy to search. See the "Null pointer checks may be optimized away more aggressively" section inhttps://gcc.gnu.org/gcc-4.9/porting_to.htmlas an example with one common implementation.
