| 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-2024-26726: btrfs: don't drop extent_map for free space inode on write error |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| btrfs: don't drop extent_map for free space inode on write error |
| |
| While running the CI for an unrelated change I hit the following panic |
| with generic/648 on btrfs_holes_spacecache. |
| |
| assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1385 |
| ------------[ cut here ]------------ |
| kernel BUG at fs/btrfs/extent_io.c:1385! |
| invalid opcode: 0000 [#1] PREEMPT SMP NOPTI |
| CPU: 1 PID: 2695096 Comm: fsstress Kdump: loaded Tainted: G W 6.8.0-rc2+ #1 |
| RIP: 0010:__extent_writepage_io.constprop.0+0x4c1/0x5c0 |
| Call Trace: |
| <TASK> |
| extent_write_cache_pages+0x2ac/0x8f0 |
| extent_writepages+0x87/0x110 |
| do_writepages+0xd5/0x1f0 |
| filemap_fdatawrite_wbc+0x63/0x90 |
| __filemap_fdatawrite_range+0x5c/0x80 |
| btrfs_fdatawrite_range+0x1f/0x50 |
| btrfs_write_out_cache+0x507/0x560 |
| btrfs_write_dirty_block_groups+0x32a/0x420 |
| commit_cowonly_roots+0x21b/0x290 |
| btrfs_commit_transaction+0x813/0x1360 |
| btrfs_sync_file+0x51a/0x640 |
| __x64_sys_fdatasync+0x52/0x90 |
| do_syscall_64+0x9c/0x190 |
| entry_SYSCALL_64_after_hwframe+0x6e/0x76 |
| |
| This happens because we fail to write out the free space cache in one |
| instance, come back around and attempt to write it again. However on |
| the second pass through we go to call btrfs_get_extent() on the inode to |
| get the extent mapping. Because this is a new block group, and with the |
| free space inode we always search the commit root to avoid deadlocking |
| with the tree, we find nothing and return a EXTENT_MAP_HOLE for the |
| requested range. |
| |
| This happens because the first time we try to write the space cache out |
| we hit an error, and on an error we drop the extent mapping. This is |
| normal for normal files, but the free space cache inode is special. We |
| always expect the extent map to be correct. Thus the second time |
| through we end up with a bogus extent map. |
| |
| Since we're deprecating this feature, the most straightforward way to |
| fix this is to simply skip dropping the extent map range for this failed |
| range. |
| |
| I shortened the test by using error injection to stress the area to make |
| it easier to reproduce. With this patch in place we no longer panic |
| with my error injection test. |
| |
| The Linux kernel CVE team has assigned CVE-2024-26726 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Fixed in 6.1.79 with commit 02f2b95b00bf57d20320ee168b30fb7f3db8e555 |
| Fixed in 6.6.18 with commit 7bddf18f474f166c19f91b2baf67bf7c5eda03f7 |
| Fixed in 6.7.6 with commit a4b7741c8302e28073bfc6dd1c2e73598e5e535e |
| Fixed in 6.8 with commit 5571e41ec6e56e35f34ae9f5b3a335ef510e0ade |
| |
| 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-2024-26726 |
| 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/btrfs/inode.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/02f2b95b00bf57d20320ee168b30fb7f3db8e555 |
| https://git.kernel.org/stable/c/7bddf18f474f166c19f91b2baf67bf7c5eda03f7 |
| https://git.kernel.org/stable/c/a4b7741c8302e28073bfc6dd1c2e73598e5e535e |
| https://git.kernel.org/stable/c/5571e41ec6e56e35f34ae9f5b3a335ef510e0ade |
