CVE-2022-49409 in Linux
Summary
by MITRE • 02/26/2025
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix bug_on in __es_tree_search
Hulk Robot reported a BUG_ON: ================================================================== kernel BUG at fs/ext4/extents_status.c:199! [...]
RIP: 0010:ext4_es_end fs/ext4/extents_status.c:199 [inline]
RIP: 0010:__es_tree_search+0x1e0/0x260 fs/ext4/extents_status.c:217 [...]
Call Trace: ext4_es_cache_extent+0x109/0x340 fs/ext4/extents_status.c:766 ext4_cache_extents+0x239/0x2e0 fs/ext4/extents.c:561 ext4_find_extent+0x6b7/0xa20 fs/ext4/extents.c:964 ext4_ext_map_blocks+0x16b/0x4b70 fs/ext4/extents.c:4384 ext4_map_blocks+0xe26/0x19f0 fs/ext4/inode.c:567 ext4_getblk+0x320/0x4c0 fs/ext4/inode.c:980 ext4_bread+0x2d/0x170 fs/ext4/inode.c:1031 ext4_quota_read+0x248/0x320 fs/ext4/super.c:6257 v2_read_header+0x78/0x110 fs/quota/quota_v2.c:63 v2_check_quota_file+0x76/0x230 fs/quota/quota_v2.c:82 vfs_load_quota_inode+0x5d1/0x1530 fs/quota/dquot.c:2368 dquot_enable+0x28a/0x330 fs/quota/dquot.c:2490 ext4_quota_enable fs/ext4/super.c:6137 [inline]
ext4_enable_quotas+0x5d7/0x960 fs/ext4/super.c:6163 ext4_fill_super+0xa7c9/0xdc00 fs/ext4/super.c:4754 mount_bdev+0x2e9/0x3b0 fs/super.c:1158 mount_fs+0x4b/0x1e4 fs/super.c:1261 [...]
==================================================================
Above issue may happen as follows: ------------------------------------- ext4_fill_super ext4_enable_quotas ext4_quota_enable ext4_iget __ext4_iget ext4_ext_check_inode ext4_ext_check __ext4_ext_check ext4_valid_extent_entries Check for overlapping extents does't take effect dquot_enable vfs_load_quota_inode v2_check_quota_file v2_read_header ext4_quota_read ext4_bread ext4_getblk ext4_map_blocks ext4_ext_map_blocks ext4_find_extent ext4_cache_extents ext4_es_cache_extent ext4_es_cache_extent __es_tree_search ext4_es_end BUG_ON(es->es_lblk + es->es_len es_lblk)
The error ext4 extents is as follows: 0af3 0300 0400 0000 00000000 extent_header 00000000 0100 0000 12000000 extent1 00000000 0100 0000 18000000 extent2 02000000 0400 0000 14000000 extent3
In the ext4_valid_extent_entries function, if prev is 0, no error is returned even if lblock<=prev. This was intended to skip the check on the first extent, but in the error image above, prev=0+1-1=0 when checking the second extent, so even though lblock<=prev, the function does not return an error. As a result, bug_ON occurs in __es_tree_search and the system panics.
To solve this problem, we only need to check that: 1. The lblock of the first extent is not less than 0. 2. The lblock of the next extent is not less than the next block of the previous extent. The same applies to extent_idx.
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Analysis
by VulDB Data Team • 02/16/2026
The vulnerability described in CVE-2022-49409 resides within the Linux kernel's ext4 file system implementation, specifically in the handling of extent trees during quota file processing. This issue manifests as a kernel BUG_ON condition that leads to system panic and potential denial of service. The flaw occurs in the ext4_ext_check_inode function which is invoked during the initialization of ext4 file systems when quota support is enabled. The problem stems from improper validation of extent entries within the extent tree structure, particularly in the ext4_valid_extent_entries function where overlapping extent checks fail to properly account for the first extent in the sequence. The vulnerability is triggered when the kernel attempts to process quota files, specifically during the v2_check_quota_file function call chain which eventually leads to the __es_tree_search function where the BUG_ON condition is evaluated. This condition checks if the end block of an extent is less than or equal to the start block, which should never occur under normal circumstances but happens due to incorrect extent validation logic.
The technical root cause of this vulnerability lies in the improper handling of extent validation logic within the ext4 file system driver. When processing extent entries, the function ext4_valid_extent_entries fails to correctly manage the prev variable during the validation process, particularly when dealing with the transition from the first extent to subsequent extents. The variable prev is initialized to zero and then incremented in a manner that does not properly account for the logical block numbers of extents, leading to a scenario where the validation logic incorrectly skips necessary checks for overlapping extents. This occurs because the code path that should validate that the start block of each extent is greater than or equal to the end block of the previous extent fails to execute properly when prev equals zero. The specific error occurs at line 199 in ext4/extents_status.c where ext4_es_end function evaluates a condition that should never be true but becomes true due to incorrect extent validation, causing the kernel to trigger a BUG_ON and subsequently panic. This validation failure is consistent with CWE-129, which describes improper validation of array indices and other forms of incorrect bounds checking, and relates to the broader category of improper input validation in kernel space operations.
The operational impact of this vulnerability is significant as it can cause complete system crashes when ext4 file systems with quota support are mounted, particularly during the initialization phase. The system panic occurs during normal file system operations when quota files are being processed, making this a critical issue for systems relying on ext4 with quota functionality. Attackers could potentially exploit this vulnerability to cause denial of service by mounting affected ext4 file systems, leading to system instability and potential data loss. The vulnerability affects all Linux kernel versions that include the problematic ext4 implementation, particularly those supporting quota functionality. The attack surface is broad as it impacts any system using ext4 file systems with quota enabled, including servers, workstations, and embedded systems. The vulnerability is particularly concerning in enterprise environments where ext4 file systems are commonly used and where system stability is paramount. The issue demonstrates a classic kernel memory corruption vulnerability that can be triggered through normal file system operations, making it difficult to prevent through traditional security measures and requiring kernel-level patches to resolve.
The fix for this vulnerability involves correcting the extent validation logic in the ext4_valid_extent_entries function to properly handle the first extent case and ensure that logical block numbers are correctly validated against previous extents. The solution requires modifying the validation to ensure that the first extent's logical block number is not less than zero, and that subsequent extents' logical block numbers are not less than the end block of the previous extent. This approach addresses the core issue by ensuring that the extent tree structure maintains proper ordering and non-overlapping properties throughout the validation process. The fix should be applied as a kernel patch to the ext4 file system driver, specifically targeting the ext4_valid_extent_entries function and related extent validation logic. Organizations should prioritize applying this patch to all systems running affected kernel versions to prevent potential system panics and maintain operational stability. The mitigation strategy should include comprehensive testing of the patched kernel on systems using ext4 with quota functionality to ensure no regressions are introduced. This vulnerability highlights the importance of proper bounds checking and validation in kernel space operations, aligning with ATT&CK technique T1068 which involves exploiting privileges through local system access, and specifically addresses the need for robust input validation in kernel modules.