PoC Index

CVE-2024-49882

HIGH 7.8EPSS 0.3%

In the Linux kernel, the following vulnerability has been resolved:ext4: fix double brelse() the buffer of the extents pathIn ext4_ext_try_to_merge_up(), set path[1].p_bh to NULL after it has beenreleased, otherwise it may be released twice. An example of what triggersthis 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 twiceFinally got the following WARRNING when removing the buffer from lru:============================================VFS: brelse: Trying to free free bufferWARNING: CPU: 2 PID: 72 at fs/buffer.c:1241 __brelse+0x58/0x90CPU: 2 PID: 72 Comm: kworker/u19:1 Not tainted 6.9.0-dirty #716RIP: 0010:__brelse+0x58/0x90Call 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[...]============================================

CVSS v3.1
7.8 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS v3.1
7.8 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS
0.32% chance of exploitation in the next 30 days, 24th percentile
Published
2024-10-21
Updated
2026-08-05

Proof-of-concept exploits (1)

References

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