| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-40955: ext4: fix slab-out-of-bounds in ext4_mb_find_good_group_avg_frag_lists() |
| |
| Description |
| =========== |
| |
| 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. |
| |
| The Linux kernel CVE team has assigned CVE-2024-40955 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.5 with commit 7e170922f06bf46effa7c57f6035fc463d6edc7e and fixed in 6.6.36 with commit 677ff4589f1501578fa903a25bb14831d0607992 |
| Issue introduced in 6.5 with commit 7e170922f06bf46effa7c57f6035fc463d6edc7e and fixed in 6.9.7 with commit b829687ae1229224262bcabf49accfa2dbf8db06 |
| Issue introduced in 6.5 with commit 7e170922f06bf46effa7c57f6035fc463d6edc7e and fixed in 6.10 with commit 13df4d44a3aaabe61cd01d277b6ee23ead2a5206 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2024-40955 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| fs/ext4/mballoc.c |
| fs/ext4/sysfs.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/677ff4589f1501578fa903a25bb14831d0607992 |
| https://git.kernel.org/stable/c/b829687ae1229224262bcabf49accfa2dbf8db06 |
| https://git.kernel.org/stable/c/13df4d44a3aaabe61cd01d277b6ee23ead2a5206 |
