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

[Baokun Li]

On 2024/12/30 15:54, Greg KH wrote:
> On Mon, Dec 30, 2024 at 03:27:45PM +0800, Baokun Li wrote:
> > > 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.
> Maybe, if so, please send the needed info to the stable list with the
> backports that have been tested.  cve@xxxxxxxxxx isn't the place for
> this :)

I replied to this thread on lore, which automatically CC's cve@xxxxxxxxxx.

We don't use these two versions, we just happened to find the issue.
If you feel that reporting issue is bothering you, then I won't do it.🙂


Regards,
Baokun