coverity null pointer dereference

Could I capture, and I would be able to glean much security information from the dump? 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. * These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. Why are players required to record the moves in World Championship Classical games? Did the drapes in old theatres actually say "ASBESTOS" on them? This has been there for decade, and was shipped in a real product. mruby is vulnerable to NULL Pointer Dereference Affected Software. Since SIZE_MAX represents the largest possible object, the largest possible string would then be SIZE_MAX-1 characters long (excluding '\0'). 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. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. Although not a critical application this prevents a real SQL injection. We were using the wrong "pages in" counter FreeBSD's ZFS port:could cause performance issues.Luckily this is not production code yet. Coverity's suggestion to fix this bug is to use a delete[] deallocator, but the concerned file is in C so that won't work. Asking for help, clarification, or responding to other answers. I say "theoretical" because I have not successfully produced strings of this length in testing. In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. This code also violates ERR33-C. Detect and handle standard library errors. What does 'They're at four. The libpng library allows applications to read, create, and manipulate PNG (Portable Network Graphics) raster image files. 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. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Furthermore, the C++20 draft (N4860) s7.6.2.1p1 says: The unary * operator performs indirection: the expression to which it is applied shall be a pointer to an object type, or a pointer to a function type and the result is an lvalue referring to the object or function to which the expression points. 33615. *var1 = 0; this dereferences the pointer, i.e. 0->member is undefined behavior. Fixed by setting name to Oh joy. Find centralized, trusted content and collaborate around the technologies you use most. Can corresponding author withdraw a paper after it has accepted without permission/acceptance of first author. Is it safe to publish research papers in cooperation with Russian academics? A common memory-leak idiom, is reallocating storage and assigning its address to a pointer that already points to allocated storage. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. I got the impression that 31 source files of Linux modules will need further adjustments. Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). Aaron:I suspect we are talking past each other. 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. If you want to change the value of your pointer, just do. Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. 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). ImmuniWeb. 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. Chains can involve more than two weaknesses, and in some cases, they might have a tree-like structure. So we have to check all the arguments before performing any actions. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Search for vulnerabilities resulting from the violation of this rule on the CERT website. Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. Thanks for contributing an answer to Stack Overflow! . That makes sense. Possible Null Pointer exception was found in a feature in which I'm the feature owner. I'm learning and will appreciate any help. 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. This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. For users who want to customize what details are displayed. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Apple. Using platform-specific means (e.g. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. NIST. FORWARD_NULL. So before writing anything to some memory location memory has to allocated to the pointer. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. int changed to size_t and if size_t parameter's is zero, allocate one word. At one point later, I get another warning: It seems like the line a_ptr->ptr = NULL is deemed incorrect/dangerous. However there is no portable way to verify that the pointer is valid, other than checking for null. If your code examples are simply searching for instances of C code of this nature. Which language's style guidelines should be used when writing code that is supposed to be called from another language? At best ISO C is under-specified in this regard, and perhaps should explicitly say so. I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called. 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. I'd guess null pointers are not valid, even though they point to 0 bytes. CalebFenton/simplify. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. This HandleRequest Function evaluates the close before checking the error. But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. Likewise, pointers to freed memory are not valid. If code1 and code2 may both be true, though, then you do have a substantial bug here. Check the results of all functions that return a value and verify that the value is non-null before acting upon it. 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. This bug was quite hard to spot! Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference. Variable "var" was uninitialized, then function that was supposed to fill it in was called. Not the answer you're looking for? That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). Off by one error: It is the third example. Making statements based on opinion; back them up with references or personal experience. ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. The null pointer check for writing or dereferencing should be a compiler flag or library setting. and Gary McGraw. SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. Common logic to perform in the middle? 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). The n=0 is a mildly interesting edge case: Clearly a pointer that points to at least one valid byte could be used as the src or dest pointer to a call to memcpy(, 0). It depends on the specific details, but in general, taking the address of any valid memory is OK. Markus:Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. 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. It looks like a logic bug, which can cause a memory leaking. The expression x.Equals(null) will throw NullReferenceException if x is null. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". Synopsys, Inc. | Policy Statement | Contact. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. What's the rationale for null terminated strings? /** In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. I see coverity defect with bold/italic code. Yes the ordering matters. Setting an incorrect jump target leads to a certain crash if the code is exercised. Category. 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? Pointer members in structs are not checked. Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. What is it that I did not understand? it may still not be enough to satisfy Coverity. Even if that memory contains a pointer which is not valid, or has been freed. Coverity complains below message: I do not understand why coverity complains here. Shouldn't the function check all pointers before dereferencing them or passing them to another function? 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). 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. 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? It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). That interpretation of the standard is not supported universally. rev2023.5.1.43405. I added a comment to explain that SIZE_MAX is the limit of size_t. We didn't figure ourselves where those threading issues came from and tried to hide them with hacks. No affinity group collision detected for cluster {}. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. View - a subset of CWE entries that provides a way of examining CWE content. Ubuntu won't accept my choice of password, Passing negative parameters to a wolframscript, Folder's list view has different sized fonts in different folders, Image of minimal degree representation of quasisimple group unique up to conjugacy. . Why does the second compliant example permit using possibly-null pointers? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Thus I became a bit more curious about involved technical details. Pittsburgh, PA 15213-2612 Canadian of Polish descent travel to Poland with Canadian passport. Coverity is correctly telling you that, albeit in a somewhat indirect way. The question is concise, clear, to-the-point and logical. 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. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Asking for help, clarification, or responding to other answers. What is it that I did not understand? 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. See "Clever Attack Exploits Fully-Patched Linux Kernel" [Goodin 2009] for an example of a code execution exploit that resulted from a null pointer dereference. To learn more, see our tips on writing great answers. I suppose there is a question of "Is a pointer that points to 0 bytes valid?" To learn more, see our tips on writing great answers. Additionally, if input_str is a null pointer, the call to strlen() dereferences a null pointer, also resulting in undefined behavior. 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. is undefined behavior (UB) if input does not actually point to a valid struct. I'm sorry if I have misunderstood the intent in your question. The 4gig boundary will probably be important too with unsigned int in LP64, but since size_t will be 64-bit, there will have to be some truncation that compilers will be able to warn on. Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? Separate it into a different function that you can call. It is kind of funny, though. Many modern techniques use data flow analysis to minimize the number of false positives. Thanks for contributing an answer to Stack Overflow! In particular, ROSE ensures that any pointer returned by malloc(), calloc(), or realloc() is first checked for NULL before being used (otherwise, it is free()-ed). 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. When this happens, CWE refers to X as "primary" to Y, and Y is "resultant" from X. 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. Why did DOS-based Windows require HIMEM.SYS to boot? Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. :). {"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. 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. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. What is the symbol (which looks similar to an equals sign) called? Passing a null pointer tomemcpy() would produce undefined behavior, even if the number of bytes to copy were 0. 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. Where does the version of Hamapil that is different from the Gemara come from? Allocated memory leaked in several cases. Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. 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. So the SIZE_MAX check was unnecessary. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. I'd really love to know why I'm being downvoted. Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? What were the most popular text editors for MS-DOS in the 1980s? ), 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. that is linked to a certain type of product, typically involving a specific language or technology. At this point we define size as strlen(input_str) + 1. 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. 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. What should I follow, if two altimeters show different altitudes? Solutions I propose: .. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. Thanks, David! There are only two condidtions in my code, cond1 and cond2. Your assertion is not backed by the wording in the standard, nor by common implementer understanding. Developer Description. NULL can't point to data. Note that it doesn't know how to check for non-heap, non-stack. <. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. Copy & paste errors might not often cause system crashes, but developer headaches. Are these quarters notes or just eighth notes? 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. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. This table shows the weaknesses and high level categories that are related to this weakness. 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. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. (I think you cover that in a different rule.) Would My Planets Blue Sun Kill Earth-Life? Alternate Terms Relationships So let me be more precise in my wording: I assert that a platform whose memcpy() did anything besides copy zero bytes when given n=0 and valid src and dest pointers was not C-standards-compliant. 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. One of the Coccinelle software maintainers expressed opposite development views today. 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. Horizontal and vertical centering in xltabular. It also uses the unsigned type size_t to pass the length parameter, ensuring that negative values are not passed to func(). Security Intelligence; Non-intrusive assessment; Developers SDK; Database . The correct idiom is to only allocate storage if the pointer is currently NULL. . 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. Category - a CWE entry that contains a set of other entries that share a common characteristic. Asking for help, clarification, or responding to other answers. // Find a VM that is breaking the affinityGroup and can be theoretically migrated, findVmViolatingPositiveAg(affinityGroup, vmToHost), org.ovirt.engine.core.dao.VmDaoImpl.getVmsByIds, Positive affinity group violation detected, Negative affinity group violation detected, // Test whether any migration is possible, this uses current AffinityGroup settings. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. That's true. accesses memory stored at its address. I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. 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). Image of minimal degree representation of quasisimple group unique up to conjugacy. of making the mruby interpreter crash, thus affecting the. Not the answer you're looking for? If the operand has type "type", the result has type "pointer to type". FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Isn't easier just to check valid range of length? We should Zoom if you wish to talk more. 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. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); Can I use an 11 watt LED bulb in a lamp rated for 8.6 watts maximum? Allowing it to be removed. It should be an ingrained practice. But no where in that particular idiom would a NULL pointer necessarily be deferenced. 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. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. May be you need to do this null check much before. @HemantBhargava - you may know that, but the code you have shown us does not ensure that. Without coverity i probably would not have found this copy&paste error. So 'decoded' will always false. The standard will simply copy 0 byteswhich is essentially a no-op. Dereferencing a null pointer is undefined behavior. valgrind wasnt that usefull because of its slowness. <<< 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. What is the symbol (which looks similar to an equals sign) called? <, [REF-1032] "Null Reference Creation and Null Pointer Dereference". By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. *var1 = 0; this dereferences the pointer, i.e. LANG.MEM.NPDLANG.STRUCT.NTADLANG.STRUCT.UPD, Null pointer dereferenceNull test after dereferenceUnchecked parameter dereference, Can detect violations of this rule.

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