CVE-2024-26794
Btrfs fiemap race vulnerability
Description
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix race between ordered extent completion and fiemap For fiemap we recently stopped locking the target extent range for the whole duration of the fiemap call, in order to avoid a deadlock in a scenario where the fiemap buffer happens to be a memory mapped range of the same file. This use case is very unlikely to be useful in practice but it may be triggered by fuzz testing (syzbot, etc). However by not locking the target extent range for the whole duration of the fiemap call we can race with an ordered extent. This happens like this: 1) The fiemap task finishes processing a file extent item that covers the file range [512K, 1M[, and that file extent item is the last item in the leaf currently being processed; 2) And ordered extent for the file range [768K, 2M[, in COW mode, completes (btrfs_finish_one_ordered()) and the file extent item covering the range [512K, 1M[ is trimmed to cover the range [512K, 768K[ and then a new file extent item for the range [768K, 2M[ is inserted in the inode's subvolume tree; 3) The fiemap task calls fiemap_next_leaf_item(), which then calls btrfs_next_leaf() to find the next leaf / item. This finds that the the next key following the one we previously processed (its type is BTRFS_EXTENT_DATA_KEY and its offset is 512K), is the key corresponding to the new file extent item inserted by the ordered extent, which has a type of BTRFS_EXTENT_DATA_KEY and an offset of 768K; 4) Later the fiemap code ends up at emit_fiemap_extent() and triggers the warning: if (cache->offset + cache->len > offset) { WARN_ON(1); return -EINVAL; } Since we get 1M > 768K, because the previously emitted entry for the old extent covering the file range [512K, 1M[ ends at an offset that is greater than the new extent's start offset (768K). This makes fiemap fail with -EINVAL besides triggering the warning that produces a stack trace like the following: [1621.677651] ------------[ cut here ]------------ [1621.677656] WARNING: CPU: 1 PID: 204366 at fs/btrfs/extent_io.c:2492 emit_fiemap_extent+0x84/0x90 [btrfs] [1621.677899] Modules linked in: btrfs blake2b_generic (...) [1621.677951] CPU: 1 PID: 204366 Comm: pool Not tainted 6.8.0-rc5-btrfs-next-151+ #1 [1621.677954] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [1621.677956] RIP: 0010:emit_fiemap_extent+0x84/0x90 [btrfs] [1621.678033] Code: 2b 4c 89 63 (...) [1621.678035] RSP: 0018:ffffab16089ffd20 EFLAGS: 00010206 [1621.678037] RAX: 00000000004fa000 RBX: ffffab16089ffe08 RCX: 0000000000009000 [1621.678039] RDX: 00000000004f9000 RSI: 00000000004f1000 RDI: ffffab16089ffe90 [1621.678040] RBP: 00000000004f9000 R08: 0000000000001000 R09: 0000000000000000 [1621.678041] R10: 0000000000000000 R11: 0000000000001000 R12: 0000000041d78000 [1621.678043] R13: 0000000000001000 R14: 0000000000000000 R15: ffff9434f0b17850 [1621.678044] FS: 00007fa6e20006c0(0000) GS:ffff943bdfa40000(0000) knlGS:0000000000000000 [1621.678046] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [1621.678048] CR2: 00007fa6b0801000 CR3: 000000012d404002 CR4: 0000000000370ef0 [1621.678053] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [1621.678055] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [1621.678056] Call Trace: [1621.678074] <TASK> [1621.678076] ? __warn+0x80/0x130 [1621.678082] ? emit_fiemap_extent+0x84/0x90 [btrfs] [1621.678159] ? report_bug+0x1f4/0x200 [1621.678164] ? handle_bug+0x42/0x70 [1621.678167] ? exc_invalid_op+0x14/0x70 [1621.678170] ? asm_exc_invalid_op+0x16/0x20 [1621.678178] ? emit_fiemap_extent+0x84/0x90 [btrfs] [1621.678253] extent_fiemap+0x766 ---truncated---
INFO
Published Date :
April 4, 2024, 9:15 a.m.
Last Modified :
April 4, 2024, 2:15 p.m.
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Remotely Exploitable :
No
Impact Score :
Exploitability Score :
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2024-26794.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2024-26794 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2024-26794 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 29, 2024
Action Type Old Value New Value -
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 14, 2024
Action Type Old Value New Value -
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Apr. 04, 2024
Action Type Old Value New Value Added Reference kernel.org https://git.kernel.org/stable/c/a1a4a9ca77f143c00fce69c1239887ff8b813bec [No types assigned] -
CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Apr. 04, 2024
Action Type Old Value New Value Added Description In the Linux kernel, the following vulnerability has been resolved: btrfs: fix race between ordered extent completion and fiemap For fiemap we recently stopped locking the target extent range for the whole duration of the fiemap call, in order to avoid a deadlock in a scenario where the fiemap buffer happens to be a memory mapped range of the same file. This use case is very unlikely to be useful in practice but it may be triggered by fuzz testing (syzbot, etc). However by not locking the target extent range for the whole duration of the fiemap call we can race with an ordered extent. This happens like this: 1) The fiemap task finishes processing a file extent item that covers the file range [512K, 1M[, and that file extent item is the last item in the leaf currently being processed; 2) And ordered extent for the file range [768K, 2M[, in COW mode, completes (btrfs_finish_one_ordered()) and the file extent item covering the range [512K, 1M[ is trimmed to cover the range [512K, 768K[ and then a new file extent item for the range [768K, 2M[ is inserted in the inode's subvolume tree; 3) The fiemap task calls fiemap_next_leaf_item(), which then calls btrfs_next_leaf() to find the next leaf / item. This finds that the the next key following the one we previously processed (its type is BTRFS_EXTENT_DATA_KEY and its offset is 512K), is the key corresponding to the new file extent item inserted by the ordered extent, which has a type of BTRFS_EXTENT_DATA_KEY and an offset of 768K; 4) Later the fiemap code ends up at emit_fiemap_extent() and triggers the warning: if (cache->offset + cache->len > offset) { WARN_ON(1); return -EINVAL; } Since we get 1M > 768K, because the previously emitted entry for the old extent covering the file range [512K, 1M[ ends at an offset that is greater than the new extent's start offset (768K). This makes fiemap fail with -EINVAL besides triggering the warning that produces a stack trace like the following: [1621.677651] ------------[ cut here ]------------ [1621.677656] WARNING: CPU: 1 PID: 204366 at fs/btrfs/extent_io.c:2492 emit_fiemap_extent+0x84/0x90 [btrfs] [1621.677899] Modules linked in: btrfs blake2b_generic (...) [1621.677951] CPU: 1 PID: 204366 Comm: pool Not tainted 6.8.0-rc5-btrfs-next-151+ #1 [1621.677954] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 [1621.677956] RIP: 0010:emit_fiemap_extent+0x84/0x90 [btrfs] [1621.678033] Code: 2b 4c 89 63 (...) [1621.678035] RSP: 0018:ffffab16089ffd20 EFLAGS: 00010206 [1621.678037] RAX: 00000000004fa000 RBX: ffffab16089ffe08 RCX: 0000000000009000 [1621.678039] RDX: 00000000004f9000 RSI: 00000000004f1000 RDI: ffffab16089ffe90 [1621.678040] RBP: 00000000004f9000 R08: 0000000000001000 R09: 0000000000000000 [1621.678041] R10: 0000000000000000 R11: 0000000000001000 R12: 0000000041d78000 [1621.678043] R13: 0000000000001000 R14: 0000000000000000 R15: ffff9434f0b17850 [1621.678044] FS: 00007fa6e20006c0(0000) GS:ffff943bdfa40000(0000) knlGS:0000000000000000 [1621.678046] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [1621.678048] CR2: 00007fa6b0801000 CR3: 000000012d404002 CR4: 0000000000370ef0 [1621.678053] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [1621.678055] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [1621.678056] Call Trace: [1621.678074] <TASK> [1621.678076] ? __warn+0x80/0x130 [1621.678082] ? emit_fiemap_extent+0x84/0x90 [btrfs] [1621.678159] ? report_bug+0x1f4/0x200 [1621.678164] ? handle_bug+0x42/0x70 [1621.678167] ? exc_invalid_op+0x14/0x70 [1621.678170] ? asm_exc_invalid_op+0x16/0x20 [1621.678178] ? emit_fiemap_extent+0x84/0x90 [btrfs] [1621.678253] extent_fiemap+0x766 ---truncated--- Added Reference kernel.org https://git.kernel.org/stable/c/d43f8e58f10a44df8c08e7f7076f3288352cd168 [No types assigned] Added Reference kernel.org https://git.kernel.org/stable/c/31d07a757c6d3430e03cc22799921569999b9a12 [No types assigned]
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2024-26794 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2024-26794
weaknesses.