Asking for help, clarification, or responding to other answers. For users who wish to see all available information for the CWE/CAPEC entry. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. Shouldn't the function check all pointers before dereferencing them or passing them to another function? Yes the ordering matters. It also adds assertions to document that certain other pointers must not be null. Synopsys, Inc. | Policy Statement | Contact. Before assigning a value you need to allocate a memory and make the pointers to point to that memory location and then assign a value. <. The issue was fixed with Avast and AVG Antivirus version 22.11 Publish Date : 2023-04-19 Last Update Date : 2023-04-19 Collapse All Expand All Select Select&Copy Scroll To Vendor . NIST. What is it that I did not understand? Thank you for clarifying your assertion until I understood it properly. extern char _etext; 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. 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. What is this brick with a round back and a stud on the side used for? The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method. The user_data pointer could be invalid in other ways, such as pointing to freed memory. The standard will simply copy 0 byteswhich is essentially a no-op. Where does the version of Hamapil that is different from the Gemara come from? 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. Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. Did the drapes in old theatres actually say "ASBESTOS" on them? Pittsburgh, PA 15213-2612
This code also violates ERR33-C. Detect and handle standard library errors. Can corresponding author withdraw a paper after it has accepted without permission/acceptance of first author. Why don't we use the 7805 for car phone chargers? Embedded hyperlinks in a thesis or research paper. At best ISO C is under-specified in this regard, and perhaps should explicitly say so. 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. When length is zero, it is probably unusable condition for this function. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); Example: tool developers, security researchers. 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. 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. There are only two condidtions in my code, cond1 and cond2. To learn more, see our tips on writing great answers. (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). 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. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. NULL can't point to data. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. Overall, I disagree with her answer, and agree with the StackOverflow response (https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be). 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. :). VM {} is NOT a viable candidate for solving affinity group violation situation. To be precise, once length is changed to a size_t and cannot take negative values, it cannot have an invalid value. Thus I became a bit more curious about involved technical details. For users who want to customize what details are displayed. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. Small typo nit: "such as if i t pointed to freed memory" meant to say "if it" instead (removing whitespace). 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. 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). 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. In my experience, there are reasons to check for a NULL pointer other than dereferencing it. How to force Unity Editor/TestRunner to run at full speed when in background? Many modern techniques use data flow analysis to minimize the number of false positives. It is pretty easy to miss such things when adding a new feature. When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. Although i'm only We haven't noticed an impact of the bug but the out of bounds access has been present since at least 2009 without anybody spotting it. of making the mruby interpreter crash, thus affecting the. The NULL check is unnecessary because the pointer can't be NULL, so the NULL check should be removed. Solution 1, it looks like, today's solution tomorrow's problem. Find centralized, trusted content and collaborate around the technologies you use most. An extremely nice thing which was discovered only by Coverity. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. Possible Null Pointer exception was found in a feature in which I'm the feature owner. 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. Identify error conditions that are not likely to occur during normal usage and trigger them. What is the symbol (which looks similar to an equals sign) called? Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. The expression x.Equals(null) will throw NullReferenceException if x is null. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Why are players required to record the moves in World Championship Classical games? It's not them. This is in the key management code which converts passwords. Not the answer you're looking for? This turned out to be a security flaw, now known as CVE-2015-3237. Can this be fixed if I reassign the *var1 to NULL again ?? I got the impression that 31 source files of Linux modules will need further adjustments. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. 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." It evaluates to true if a_ptr is not NULL. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. Thanks for this checker. large number of packets leads to NULL dereference, packet with invalid error status value triggers NULL dereference, Chain: race condition for an argument value, possibly resulting in NULL dereference. SIZE_MAX is the largest possible value that a size_t could take, so it is not possible to have anything larger than SIZE_MAX. patch id. accesses memory stored at its address. Folder's list view has different sized fonts in different folders. Making statements based on opinion; back them up with references or personal experience. This one is pretty awesome. 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. Dereferencing a pointer that might be null " findVmViolatingPositiveAg(affinityGroup, vmToHost) " when calling " getVmsByIds . Which language's style guidelines should be used when writing code that is supposed to be called from another language? It could cause e-mails stored with incorrect names. Thanks for contributing an answer to Stack Overflow! Not the answer you're looking for? This compliant solution eliminates the null pointer deference by initializing sk to tun->sk following the null pointer check. Markus:Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. Use automated static analysis tools that target this type of weakness. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. @HemantBhargava - you may know that, but the code you have shown us does not ensure that. Security Intelligence; Non-intrusive assessment; Developers SDK; Database . (In contrast, the case of passing 0 bytes to malloc is addressed in C11.) Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? This code will definitely crash due to a null pointer dereference in certain cases. 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?). 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. A boy can regenerate, so demons eat him for years. Right? Yeah, I suspect once it's possible to allocate 2+gigs contiguously in amainstream install of a modern OS, we'll see a frenzy of new vulnerabilities come out. Loading. This HandleRequest Function evaluates the close before checking the error. It modifies the pointed-to data. Likewise, pointers to freed memory are not valid. <, [REF-1033] "NULL Pointer Dereference [CWE-476]". "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". FORWARD_NULL. And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). I'd guess WG14 has considered these questions, but I haven't until now :). On many platforms, dereferencing a null pointer results inabnormal program termination, but this is not required by the standard. 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. * @param vmToHost vm to host assignments What is this brick with a round back and a stud on the side used for? Could I capture, and I would be able to glean much security information from the dump? The platform does add offsetof( struct_type, member) to input and dereferences that. To fix the bug in the code and also make Coverity happy, as suggested by derHugo in a comment, change the RemoveAll line to something like this: Thanks for contributing an answer to Stack Overflow! IMHO, the rule title should be changed to something less general. Assign an array of Swift strings to a C structure variable taking a char ** value. NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. Making statements based on opinion; back them up with references or personal experience. Do you find another previous clarification approach interesting and helpful? Off by one error: It is the third example. More specific than a Pillar Weakness, but more general than a Base Weakness. Dereferencing a null pointer always results in undefined behavior and can cause crashes. Which language's style guidelines should be used when writing code that is supposed to be called from another language? Right? 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. Because null pointer dereferencing is UB, the if (!tun) check can be elided entirely by the optimizer (since the tun->sk implies that tun must be non-null). accesses memory stored at its address. I added an assertion to that compliant code example. 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. Copy the n-largest files from a certain directory to the current one. What's the rationale for null terminated strings? If input is null, that is technically not a null dereference. It is always true that if E is a function designator or an lvalue that is a valid operand of the unary & operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. The question is concise, clear, to-the-point and logical. Coverity scan helps our developers finding issues like these. The pointer could in fact be NULL and any dereference prior to that NULL check could result in a NULL pointer dereference, so you need to either do the NULL check sooner or don't deereference at that point. 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. Developer Description. ImmuniWeb. Full description here: http://curl.haxx.se/docs/adv_20150617B.html It could make a malicious server fool a client to send off data from Prototypical copy-paste error. Note that this code is also vulnerable to a buffer overflow (CWE-119). valgrind wasnt that usefull because of its slowness. NIST Workshop on Software Security Assurance Tools Techniques and Metrics. .. 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. It modifies the pointed-to data. Does &((struct name *)NULL -> b) cause undefined behaviour in C11? 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! The two languages try to maximize compatibility, and occasionally succeed. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. return p == NULL || (char *)p < &_etext; This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. In Coverity, FORWARD_NULL reports defects when there are enough evidences to be sure the null access will (can) happen. Common logic to perform in the middle? 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. View Defect : ScummVM: OVERRUN: C/C++: Memory - illegal accesses: Realy nice catch by Coverity. that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. Improve INSERT-per-second performance of SQLite. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory? *var1 = 0; this dereferences the pointer, i.e. This table shows the weaknesses and high level categories that are related to this weakness. Checker. And in this step. It looks like a logic bug, which can cause a memory leaking. I've changed it to say null pointer instead of invalid pointer. Buffer overflow difficult to find by reading the code that would result a crash if path is too long. *var1 = 0; this dereferences the pointer, i.e. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. Overview. Search for vulnerabilities resulting from the violation of this rule on the CERT website. Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? Standing by. There are other problems with this code, as is noted in the rule. WG21 (the C++ working group) may wish to define 0->y, and they are within their right to do so. In your case you are not doing it,so you have a segmentation fault(or crash) . User without create permission can create a custom object from Managed package using Custom Rest API. 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? Dereferencing a null pointer is undefined behavior. The exact line that helped in your answer was this - "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. Monitor the software for any unexpected behavior. Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. Only irrelevant information has been removed. * Select VMs from the broken affinity group that are running on the same host. You need to show more code along with what static analysis tool you are using for us to be able to give an answer to you. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. This was potentially problematic, due to the assert on an uninitialized variable. that is linked to a certain type of product, typically involving a specific language or technology. Why don't we use the 7805 for car phone chargers? This solution also ensures that theuser_data pointer is not null. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. Null pointer dereferences. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. CPE Name Name Version; mruby: 3.1.0: Products. This fixed weird behaviour that was really hard to find. ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. Example: tool developers, security researchers, pen-testers, incident response analysts. Carnegie Mellon University
This fault is buried deep within some complex logic that makes it really hard to track. 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). rev2023.5.1.43405. This vulnerability is capable. I'd guess null pointers are not valid, even though they point to 0 bytes. This defect on our template caused null pointer deferencing in over hundred use cases. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy(). 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]. Connect and share knowledge within a single location that is structured and easy to search. 412-268-5800, 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 pointer. That exception could have rendered the entire feature non operational (And many log messages that Unused value and previous write overwriting found in the defect meant error in algorithm. Coverity found a case where a copy/paste action went wrong. 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. This information is often useful in understanding where a weakness fits within the context of external information sources. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. 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. NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. I've posted an example for the sake of completion-. It does not give the pointer a new value. * @return a list of vms which are candidates for migration Canadian of Polish descent travel to Poland with Canadian passport. can have the value zero on a call to that function. 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. This listing shows possible areas for which the given weakness could appear. The choice could be made to use a language that is not susceptible to these issues. 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. Category. But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. with solve of this bug problems have gone. ), 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. If code1 and code2 may both be true, though, then you do have a substantial bug here. 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! Making statements based on opinion; back them up with references or personal experience. Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. Did the drapes in old theatres actually say "ASBESTOS" on them? Apple. then the UB is not in your code, you just may be searching for code with potential UB. Aaron:I suspect we are talking past each other. Typical "easy to spot if you know there is a problem error". Thanks for the reference to Julia Lawall's response to your question. Pointer members in structs are not checked. The null pointer check for writing or dereferencing should be a compiler flag or library setting. It seems that my understanding needs also to grow for such information. it may still not be enough to satisfy Coverity. I'm learning and will appreciate any help.
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