CVE-2024-40955: ext4: fix slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists()
First published: Fri Jul 12 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: ext4: fix slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists() We can trigger a slab-out-of-bounds with the following commands: mkfs.ext4 -F /dev/$disk 10G mount /dev/$disk /tmp/test echo 2147483647 > /sys/fs/ext4/$disk/mb_group_prealloc echo test > /tmp/test/file && sync ================================================================== BUG: KASAN: slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists+0x8a/0x200 [ext4] Read of size 8 at addr ffff888121b9d0f0 by task kworker/u2:0/11 CPU: 0 PID: 11 Comm: kworker/u2:0 Tainted: GL 6.7.0-next-20240118 #521 Call Trace: dump_stack_lvl+0x2c/0x50 kasan_report+0xb6/0xf0 ext4_mb_find_good_group_avg_frag_lists+0x8a/0x200 [ext4] ext4_mb_regular_allocator+0x19e9/0x2370 [ext4] ext4_mb_new_blocks+0x88a/0x1370 [ext4] ext4_ext_map_blocks+0x14f7/0x2390 [ext4] ext4_map_blocks+0x569/0xea0 [ext4] ext4_do_writepages+0x10f6/0x1bc0 [ext4] [...] ================================================================== The flow of issue triggering is as follows: // Set s_mb_group_prealloc to 2147483647 via sysfs ext4_mb_new_blocks ext4_mb_normalize_request ext4_mb_normalize_group_request ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc ext4_mb_regular_allocator ext4_mb_choose_next_group ext4_mb_choose_next_group_best_avail mb_avg_fragment_size_order order = fls(len) - 2 = 29 ext4_mb_find_good_group_avg_frag_lists frag_list = &sbi->s_mb_avg_fragment_size[order] if (list_empty(frag_list)) // Trigger SOOB! At 4k block size, the length of the s_mb_avg_fragment_size list is 14, but an oversized s_mb_group_prealloc is set, causing slab-out-of-bounds to be triggered by an attempt to access an element at index 29. Add a new attr_id attr_clusters_in_group with values in the range [0, sbi->s_clusters_per_group] and declare mb_group_prealloc as that type to fix the issue. In addition avoid returning an order from mb_avg_fragment_size_order() greater than MB_NUM_ORDERS(sb) and reduce some useless loops.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Linux kernel | >=6.5<6.6.36 | |
| Linux Linux kernel | >=6.7<6.9.7 | |
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.119-1 6.11.10-1 6.12.5-1 |
Never miss a vulnerability like this again
Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.
Reference Links
- https://git.kernel.org/stable/c/13df4d44a3aaabe61cd01d277b6ee23ead2a5206
- https://git.kernel.org/stable/c/677ff4589f1501578fa903a25bb14831d0607992
- https://git.kernel.org/stable/c/b829687ae1229224262bcabf49accfa2dbf8db06
- https://git.kernel.org/linus/13df4d44a3aaabe61cd01d277b6ee23ead2a5206
- https://security-tracker.debian.org/tracker/CVE-2024-40955
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-40955
- https://nvd.nist.gov/vuln/detail/CVE-2024-40955
- https://launchpad.net/bugs/cve/CVE-2024-40955
- https://ubuntu.com/security/CVE-2024-40955
- agent/title
- agent/type
- collector/nvd-api
- source/NVD
- agent/software-canonical-lookup
- agent/severity
- agent/weakness
- agent/remedy
- agent/author
- agent/first-publish-date
- agent/references
- agent/tags
- collector/usn-cve
- source/Ubuntu
- agent/description
- collector/nvd-cve
- agent/event
- collector/security-tracker-debian
- source/Debian
- agent/softwarecombine
- collector/mitre-cve
- source/MITRE
- agent/last-modified-date
- agent/trending
- vendor/linux
- canonical/linux linux kernel
- version/linux linux kernel/6.5
- version/linux linux kernel/6.7
- package-manager/debian