Re: CVE-2024-50191: ext4: don't set SB_RDONLY after filesystem errors

Baokun Li
2024-12-30T07:27:54Z

> Description
> ===========
>
> In the Linux kernel, the following vulnerability has been resolved:
>
> ext4: don't set SB_RDONLY after filesystem errors
>
> When the filesystem is mounted with errors=remount-ro, we were setting
> SB_RDONLY flag to stop all filesystem modifications. We knew this misses
> proper locking (sb->s_umount) and does not go through proper filesystem
> remount procedure but it has been the way this worked since early ext2
> days and it was good enough for catastrophic situation damage
> mitigation. Recently, syzbot has found a way (see link) to trigger
> warnings in filesystem freezing because the code got confused by
> SB_RDONLY changing under its hands. Since these days we set
> EXT4_FLAGS_SHUTDOWN on the superblock which is enough to stop all
> filesystem modifications, modifying SB_RDONLY shouldn't be needed. So
> stop doing that.
>
> The Linux kernel CVE team has assigned CVE-2024-50191 to this issue.
>
>
> Affected and fixed versions
> ===========================
>
>     Fixed in 5.15.168 with commit fbb177bc1d64
>     Fixed in 6.1.113 with commit 4061e07f040a

Since 6.1 and 5.15 don't have backport
commit 95257987a638 ("ext4: drop EXT4_MF_FS_ABORTED flag"),
we won't set the EXT4_FLAGS_SHUTDOWN bit in ext4_handle_error() yet. So
here these two commits cause us to repeatedly get the following printout:

[   42.993195] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993351] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993483] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993597] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993638] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993718] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993866] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993874] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.993874] EXT4-fs error (device sda) in __ext4_new_inode:1089:
Journal has aborted
[   42.994059] EXT4-fs error (device sda): ext4_journal_check_start:83:
comm fsstress: Detected aborted journal
[   42.999893] EXT4-fs: 58002 callbacks suppressed
[   42.999895] EXT4-fs (sda): Remounting filesystem read-only
[   43.000110] EXT4-fs (sda): Remounting filesystem read-only
[   43.000274] EXT4-fs (sda): Remounting filesystem read-only
[   43.000421] EXT4-fs (sda): Remounting filesystem read-only
[   43.000569] EXT4-fs (sda): Remounting filesystem read-only
[   43.000701] EXT4-fs (sda): Remounting filesystem read-only
[   43.000869] EXT4-fs (sda): Remounting filesystem read-only
[   43.001094] EXT4-fs (sda): Remounting filesystem read-only
[   43.001229] EXT4-fs (sda): Remounting filesystem read-only
[   43.001365] EXT4-fs (sda): Remounting filesystem read-only

Perhaps we should revert both commits.

Thanks,
Baokun

>     Fixed in 6.6.57 with commit 58c0648e4c77
>     Fixed in 6.11.4 with commit ee77c3884691
>     Fixed in 6.12-rc1 with commit d3476f3dad4a
>
> 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-2024-50191
> 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/super.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/fbb177bc1d6487cd3e9b50ae0be2781b7297980d
> https://git.kernel.org/stable/c/4061e07f040a091f694f461b86a26cf95ae66439
> https://git.kernel.org/stable/c/58c0648e4c773f5b54f0cb63bc8c7c6bf52719a9
> https://git.kernel.org/stable/c/ee77c388469116565e009eaa704a60bc78489e09
> https://git.kernel.org/stable/c/d3476f3dad4ad68ae5f6b008ea6591d1520da5d8