UBUNTU-CVE-2024-49882
In the Linux kernel, the following vulnerability has been resolved: ext4: fix double brelse() the buffer of the extents path In ext4_ext_try_to_merge_up(), set path[1].p_bh to NULL after it has been released, otherwise it may be released twice. An example of what triggers this is as follows: split2 map split1 |--------|-------|--------| ext4_ext_map_blocks ext4_ext_handle_unwritten_extents ext4_split_convert_extents // path->p_depth == 0 ext4_split_extent // 1. do split1 ext4_split_extent_at |ext4_ext_insert_extent | ext4_ext_create_new_leaf | ext4_ext_grow_indepth | le16_add_cpu(&neh->eh_depth, 1) | ext4_find_extent | // return -ENOMEM |// get error and try zeroout |path = ext4_find_extent | path->p_depth = 1 |ext4_ext_try_to_merge | ext4_ext_try_to_merge_up | path->p_depth = 0 | brelse(path[1].p_bh) ---> not set to NULL here |// zeroout success // 2. update path ext4_find_extent // 3. do split2 ext4_split_extent_at ext4_ext_insert_extent ext4_ext_create_new_leaf ext4_ext_grow_indepth le16_add_cpu(&neh->eh_depth, 1) ext4_find_extent path[0].p_bh = NULL; path->p_depth = 1 read_extent_tree_block ---> return err // path[1].p_bh is still the old value ext4_free_ext_path ext4_ext_drop_refs // path->p_depth == 1 brelse(path[1].p_bh) ---> brelse a buffer twice Finally got the following WARRNING when removing the buffer from lru: ============================================ VFS: brelse: Trying to free free buffer WARNING: CPU: 2 PID: 72 at fs/buffer.c:1241 __brelse+0x58/0x90 CPU: 2 PID: 72 Comm: kworker/u19:1 Not tainted 6.9.0-dirty #716 RIP: 0010:__brelse+0x58/0x90 Call Trace: <TASK> __find_get_block+0x6e7/0x810 bdev_getblk+0x2b/0x480 __ext4_get_inode_loc+0x48a/0x1240 ext4_get_inode_loc+0xb2/0x150 ext4_reserve_inode_write+0xb7/0x230 __ext4_mark_inode_dirty+0x144/0x6a0 ext4_ext_insert_extent+0x9c8/0x3230 ext4_ext_map_blocks+0xf45/0x2dc0 ext4_map_blocks+0x724/0x1700 ext4_do_writepages+0x12d6/0x2a70 [...] ============================================
02 / AFFECTED SOFTWARE
Affected packages
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: ext4: fix double brelse() the buffer of the extents path In ext4_ext_try_to_merge_up(), set path[1].p_bh to NULL after it has been released, otherwise it may be released twice. An example of what triggers this is as follows: split2 map split1 |--------|-------|--------| ext4_ext_map_blocks ext4_ext_handle_unwritten_extents ext4_split_convert_extents // path->p_depth == 0 ext4_split_extent // 1. do split1 ext4_split_extent_at |ext4_ext_insert_extent | ext4_ext_create_new_leaf | ext4_ext_grow_indepth | le16_add_cpu(&neh->eh_depth, 1) | ext4_find_extent | // return -ENOMEM |// get error and try zeroout |path = ext4_find_extent | path->p_depth = 1 |ext4_ext_try_to_merge | ext4_ext_try_to_merge_up | path->p_depth = 0 | brelse(path[1].p_bh) ---> not set to NULL here |// zeroout success // 2. update path ext4_find_extent // 3. do split2 ext4_split_extent_at ext4_ext_insert_extent ext4_ext_create_new_leaf ext4_ext_grow_indepth le16_add_cpu(&neh->eh_depth, 1) ext4_find_extent path[0].p_bh = NULL; path->p_depth = 1 read_extent_tree_block ---> return err // path[1].p_bh is still the old value ext4_free_ext_path ext4_ext_drop_refs // path->p_depth == 1 brelse(path[1].p_bh) ---> brelse a buffer twice Finally got the following WARRNING when removing the buffer from lru: ============================================ VFS: brelse: Trying to free free buffer WARNING: CPU: 2 PID: 72 at fs/buffer.c:1241 __brelse+0x58/0x90 CPU: 2 PID: 72 Comm: kworker/u19:1 Not tainted 6.9.0-dirty #716 RIP: 0010:__brelse+0x58/0x90 Call Trace: <TASK> __find_get_block+0x6e7/0x810 bdev_getblk+0x2b/0x480 __ext4_get_inode_loc+0x48a/0x1240 ext4_get_inode_loc+0xb2/0x150 ext4_reserve_inode_write+0xb7/0x230 __ext4_mark_inode_dirty+0x144/0x6a0 ext4_ext_insert_extent+0x9c8/0x3230 ext4_ext_map_blocks+0xf45/0x2dc0 ext4_map_blocks+0x724/0x1700 ext4_do_writepages+0x12d6/0x2a70 [...] ============================================
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/dcaa6c31134c0f515600111c38ed7750003e1b9c
- https://git.kernel.org/stable/c/230ee0535d01478bad9a3037292043f39b9be10b
- https://git.kernel.org/stable/c/32bbb59e3f18facd7201bef110010bf35819b8c3
- https://git.kernel.org/stable/c/68a69cf60660c73990c1875f94a5551600b04775
- https://git.kernel.org/stable/c/7633407ca4ab8be2916ab214eb44ccebc6a50e1a
- https://git.kernel.org/stable/c/78bbc3d15b6f443acb26e94418c445bac940d414
- https://git.kernel.org/stable/c/b6c29c8f3d7cb67b505f3b2f6c242d52298d1f2e
- https://git.kernel.org/stable/c/dcaa6c31134c0f515600111c38ed7750003e1b9c
- https://ubuntu.com/security/CVE-2024-49882
- https://ubuntu.com/security/notices/USN-7166-1
- https://ubuntu.com/security/notices/USN-7166-2
- https://ubuntu.com/security/notices/USN-7166-3
- https://ubuntu.com/security/notices/USN-7166-4
- https://ubuntu.com/security/notices/USN-7186-1
- https://ubuntu.com/security/notices/USN-7186-2
- https://ubuntu.com/security/notices/USN-7194-1
- https://ubuntu.com/security/notices/USN-7276-1
- https://ubuntu.com/security/notices/USN-7277-1
- https://ubuntu.com/security/notices/USN-7293-1
- https://ubuntu.com/security/notices/USN-7294-1
- https://ubuntu.com/security/notices/USN-7294-2
- https://ubuntu.com/security/notices/USN-7294-3
- https://ubuntu.com/security/notices/USN-7294-4
- https://ubuntu.com/security/notices/USN-7295-1
- https://ubuntu.com/security/notices/USN-7301-1
- https://ubuntu.com/security/notices/USN-7303-1
- https://ubuntu.com/security/notices/USN-7303-2
- https://ubuntu.com/security/notices/USN-7303-3
- https://ubuntu.com/security/notices/USN-7304-1
- https://ubuntu.com/security/notices/USN-7310-1
- https://ubuntu.com/security/notices/USN-7311-1
- https://ubuntu.com/security/notices/USN-7384-1
- https://ubuntu.com/security/notices/USN-7384-2
- https://ubuntu.com/security/notices/USN-7385-1
- https://ubuntu.com/security/notices/USN-7386-1
- https://ubuntu.com/security/notices/USN-7393-1
- https://ubuntu.com/security/notices/USN-7401-1
- https://ubuntu.com/security/notices/USN-7403-1
- https://ubuntu.com/security/notices/USN-7413-1
- https://ubuntu.com/security/notices/USN-7468-1
- https://ubuntu.com/security/notices/USN-7539-1
- https://ubuntu.com/security/notices/USN-7540-1
- https://www.cve.org/CVERecord?id=CVE-2024-49882