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. I would also guess that pointers that point to the one-past-the-end of an array are also invalid. We didn't figure ourselves where those threading issues came from and tried to hide them with hacks. Only irrelevant information has been removed. The standard will simply copy 0 byteswhich is essentially a no-op. 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. This table specifies different individual consequences associated with the weakness. IMHO, the rule title should be changed to something less general. On many platforms, dereferencing a null pointer results inabnormal program termination, but this is not required by the standard. I'm sorry if I have misunderstood the intent in your question. <. Would you like to help any further according to different understanding and expectations for affected implementation details. 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. It does not give the pointer a new 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. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. /** Finally, Clang and Coccinelle are part of the LLVM project, which will define some of the undefined behaviors in C++. This HandleRequest Function evaluates the close before checking the error. how to remove a project from coverity-scan, Remove duplicate results from multiple Coverity runs, Coverity. This bug ONLY surfaces when debugging or running the program with her verbosity. The occurrence of this wrong index was not seen in the code. 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. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of its operand. A boy can regenerate, so demons eat him for years. I added an assertion to that compliant code example. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. 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. Ah, gotcha. that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. 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. mruby is vulnerable to NULL Pointer. Making statements based on opinion; back them up with references or personal experience. Can I use the spell Immovable Object to create a castle which floats above the clouds? We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. 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. It should be an ingrained practice. Why refined oil is cheaper than cold press oil? Connect and share knowledge within a single location that is structured and easy to search. cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". The two languages try to maximize compatibility, . If malloc() fails, it returns a null pointer that is assigned to c_str. If you are working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? specifies the length of the array for a function. (I think you cover that in a different rule.) The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). It worked normally, but sometimes devices had cryptic types. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. The above check can't hurt, as I guess you could have a system with a 32-bit size_t that had a ton of memory and had some crazy banking/selector scheme with pointers. Extended Description NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? That interpretation of the standard is not supported universally. ', referring to the nuclear power plant in Ignalina, mean? Chain: Use of an unimplemented network socket operation pointing to an uninitialized handler function (, Chain: race condition might allow resource to be released before operating on it, leading to NULL dereference, Chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference, Chain: IP and UDP layers each track the same value with different mechanisms that can get out of sync, possibly resulting in a NULL dereference, Chain: uninitialized function pointers can be dereferenced allowing code execution, Chain: improper initialization of memory can lead to NULL dereference, Chain: game server can access player data structures before initialization has happened leading to NULL dereference, Chain: The return value of a function returning a pointer is not checked for success (, Chain: a message having an unknown message type may cause a reference to uninitialized memory resulting in a null pointer dereference (, Chain: unchecked return value can lead to NULL dereference. 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. Is it safe to publish research papers in cooperation with Russian academics? Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. 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). 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. But passing 0 to memcpy() is not one of them. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Embedded hyperlinks in a thesis or research paper. I believe in this case, either expression would work. 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. 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. NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. 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. DATABASE RESOURCES PRICING ABOUT US. rev2023.5.1.43405. Why is this claimed dereferencing type-punned pointer warning compiler-specific? Check the results of all functions that return a value and verify that the value is non-null before acting upon it. So 'decoded' will always false. One situation this can happen is when the pointer has been checked against NULL and is dereferenced later. 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. So we have to check all the arguments before performing any actions. In this case, the difference is the assumption thatmalloc() always returns non-nullfor the second NCCE, whereas the first NCCE has themalloc() abstracted away. 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. There are other problems with this code, as is noted in the rule. Not the answer you're looking for? The final NCCE is actually more insidious than it seems at first. New feature implementation got stuck for days because old code had obscure implementation which caused debuging nightmare. Thanks for the reference to Julia Lawall's response to your question. It evaluates to true if a_ptr is not NULL. .. 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. 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 correct idiom is to only allocate storage if the pointer is currently NULL. Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values. ), [REF-6] Katrina Tsipenyuk, Brian Chess 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. 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. Variable "var" was uninitialized, then function that was supposed to fill it in was called. Generating points along line with specifying the origin of point generation in QGIS. Category. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. If you want to change the value of your pointer, just do. To be precise, once length is changed to a size_t and cannot take negative values, it cannot have an invalid value. 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. 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. uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). Simple and excellent job. It modifies the pointed-to data. Is there a generic term for these trajectories? 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. SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? What should I follow, if two altimeters show different altitudes? parsing /proc/self/maps under linux) one might find out whether the pointer points into mapped memory, but this is still not a guarantee of validity because it is very coarse-grained see again the above example. If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. this patch have merged in upstream master branch. And in this case, there is no pointed-to data. @HemantBhargava - you may know that, but the code you have shown us does not ensure that. 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. 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! This table shows the weaknesses and high level categories that are related to this weakness. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. This turned out to be a security flaw, now known as CVE-2015-3237. void host_lookup(char *user_supplied_addr){, if("com.example.URLHandler.openURL".equals(intent.getAction())) {. Making statements based on opinion; back them up with references or personal experience. To learn more, see our tips on writing great answers. Canadian of Polish descent travel to Poland with Canadian passport. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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). 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). :). ), 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. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). 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. I note with interest, that ISO C does permit &*x when x is null. And in this step. More information is available Please edit the custom filter or select a different filter. Is this a false positive from Coverity or should I do something to fix this? The platform does add offsetof( struct_type, member) to input and dereferences that. 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. Possible Null Pointer exception was found in a feature in which I'm the feature owner. can have the value zero on a call to that function. 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. It looks like a logic bug, which can cause a memory leaking. What does 'They're at four. Configure coverity to check that a declared variable is initialized before usage as a pointer. Connect and share knowledge within a single location that is structured and easy to search. 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. In the following code, the programmer assumes that the system always has a property named "cmd" defined. 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. Hence the error. I say "theoretical" because I have not successfully produced strings of this length in testing. That's true. Otherwise, the result is a pointer to the object or function designated by its operand. 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. Many platforms can support testing for those also. This compliant solution eliminates the null pointer deference by initializing sk to tun->sk following the null pointer check. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); 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. Coverity is giving you a warning because you are in fact doing a NULL check: Here, a_ptr is evaluated in a boolean context. 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). NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. 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. Use of the Common Weakness Enumeration (CWE) and the associated references from this website are subject to the Terms of Use. Markus:Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. To learn more, see our tips on writing great answers. Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage. Is there any known 80-bit collision attack? 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. This compliant solution ensures that the pointer returned by png_malloc() is not null. Did the drapes in old theatres actually say "ASBESTOS" on them? Does &((struct name *)NULL -> b) cause undefined behaviour in C11? that is linked to a certain type of product, typically involving a specific language or technology. The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. Note that this code is also vulnerable to a buffer overflow (CWE-119). This solution also ensures that theuser_data pointer is not null. The null pointer check for writing or dereferencing should be a compiler flag or library setting. I believe that dereferencing NULL should not crash the system, should not allow a write to a NULL pointer area, but should always set errno, If I am a hacker, could I trap a null failure that would force a memory dump. 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. 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. 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. There are only two condidtions in my code, cond1 and cond2. NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. View Defect : ScummVM: OVERRUN: C/C++: Memory - illegal accesses: Realy nice catch by Coverity. and Gary McGraw. 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. It's not them. int changed to size_t and if size_t parameter's is zero, allocate one word. One weakness, X, can directly create the conditions that are necessary to cause another weakness, Y, to enter a vulnerable condition. mruby is vulnerable to NULL Pointer. 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 this happens, CWE refers to X as "primary" to Y, and Y is "resultant" from X. Thank you for clarifying your assertion until I understood it properly. This code will definitely crash due to a null pointer dereference in certain cases. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. Description. The sk pointer is initialized to tun->sk before checking if tun is a null pointer. then the UB is not in your code, you just may be searching for code with potential UB. 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]. It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). Made code more compliant with other rules. Software Engineering Institute In your case you are not doing it,so you have a segmentation fault(or crash) . It can never evaluate to true (unless Equals has been overridden to do something screwy). Where does the version of Hamapil that is different from the Gemara come from? availability of the system. Either the check against null is unnecessary, or there may be a null pointer dereference. *var1 = 0; this dereferences the pointer, i.e. Search for vulnerabilities resulting from the violation of this rule on the CERT website. At one point later, I get another warning: It seems like the line a_ptr->ptr = NULL is deemed incorrect/dangerous. NIST. This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member.
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