CVE-2022-49879 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix BUG_ON() when directory entry has invalid rec_len
The rec_len field in the directory entry has to be a multiple of 4. A corrupted filesystem image can be used to hit a BUG() in ext4_rec_len_to_disk(), called from make_indexed_dir().
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kernel BUG at fs/ext4/ext4.h:2413! ... RIP: 0010:make_indexed_dir+0x53f/0x5f0 ... Call Trace: <TASK> ? add_dirent_to_buf+0x1b2/0x200 ext4_add_entry+0x36e/0x480 ext4_add_nondir+0x2b/0xc0 ext4_create+0x163/0x200 path_openat+0x635/0xe90 do_filp_open+0xb4/0x160 ? __create_object.isra.0+0x1de/0x3b0 ? _raw_spin_unlock+0x12/0x30 do_sys_openat2+0x91/0x150 __x64_sys_open+0x6c/0xa0 do_syscall_64+0x3c/0x80 entry_SYSCALL_64_after_hwframe+0x46/0xb0
The fix simply adds a call to ext4_check_dir_entry() to validate the directory entry, returning -EFSCORRUPTED if the entry is invalid.
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Analysis
by VulDB Data Team • 03/14/2026
The vulnerability described in CVE-2022-49879 represents a critical flaw in the Linux kernel's ext4 filesystem implementation that could lead to system instability and potential denial of service conditions. This issue specifically affects the directory entry handling mechanism within the ext4 filesystem driver, where a malformed rec_len field in directory entries can trigger a kernel BUG_ON() condition that results in system crashes. The vulnerability stems from insufficient validation of directory entry structures during filesystem operations, particularly when processing indexed directories. The flaw manifests when a corrupted filesystem image contains directory entries with invalid rec_len values that are not multiples of 4, which violates the ext4 filesystem specification and expected data structure alignment requirements.
The technical execution of this vulnerability occurs through the ext4_rec_len_to_disk() function which is invoked from make_indexed_dir(), a function responsible for creating indexed directory structures. When the kernel encounters a directory entry with an invalid rec_len field that does not conform to the required 4-byte alignment, the BUG_ON() macro triggers a kernel panic, causing the system to halt execution. The call trace demonstrates the execution path leading to this condition through normal filesystem operations including file creation and directory traversal. The vulnerability specifically targets the filesystem layer where directory entries are processed, making it particularly dangerous as it can be triggered during routine file system operations and potentially exploited by malicious actors with access to corrupted filesystem images or through crafted inputs that manipulate directory structures.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a potential vector for denial of service attacks against Linux systems running ext4 filesystems. The vulnerability affects systems where ext4 filesystems are used for storing user data, system files, or application data, particularly in server environments where continuous operation is critical. When triggered, the BUG_ON() condition causes immediate system instability, requiring manual intervention to recover from the crash. The vulnerability also highlights a broader security concern regarding filesystem corruption handling, as it demonstrates how malformed data structures can lead to kernel-level failures rather than graceful error handling. The fix implemented addresses this by adding proper validation through ext4_check_dir_entry() which ensures that directory entries meet the required formatting standards before processing, returning appropriate error codes instead of causing kernel panics.
The fix for CVE-2022-49879 aligns with security best practices for robust input validation and defensive programming principles, specifically addressing CWE-129 Improper Validation of Array Index and CWE-248 Unchecked Error Condition. This vulnerability demonstrates the importance of proper error handling in kernel space operations and the necessity of validating all input data before processing, particularly in filesystem drivers where malformed data can originate from various sources including disk corruption, malicious inputs, or software bugs. The implementation of ext4_check_dir_entry() validation follows established security patterns recommended in the ATT&CK framework for kernel-level defenses, specifically addressing the persistence and privilege escalation categories by preventing malicious actors from leveraging filesystem corruption to gain unauthorized system access or cause system instability. This fix represents a critical improvement in kernel robustness and aligns with the principle of fail-safe design, ensuring that filesystem operations handle malformed data gracefully rather than causing system-wide failures. The vulnerability and its resolution highlight the ongoing need for comprehensive filesystem validation mechanisms and proper error handling in operating system kernels to maintain system stability and security.