Re: CVE-2024-36966: erofs: reliably distinguish block based and fscache mode

[Baokun Li]

On 2024/6/13 21:55, Greg Kroah-Hartman wrote:
> On Thu, Jun 13, 2024 at 07:21:14PM +0800, Baokun Li wrote:
> > On 2024/6/13 17:38, Gao Xiang wrote:
> > > Hi,
> > >
> > > (+Cc Baokun Li)
> > >
> > > On 2024/6/8 20:53, Greg Kroah-Hartman wrote:
> > > > Description
> > > > ===========
> > > >
> > > > In the Linux kernel, the following vulnerability has been resolved:
> > > >
> > > > erofs: reliably distinguish block based and fscache mode
> > > >
> > > > When erofs_kill_sb() is called in block dev based mode, s_bdev may not
> > > > have been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled,
> > > > it will be mistaken for fscache mode, and then attempt to free an
> > > > anon_dev
> > > > that has never been allocated, triggering the following warning:
> > > >
> > > > ============================================
> > > > ida_free called for id=0 which is not allocated.
> > > > WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
> > > > Modules linked in:
> > > > CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
> > > > RIP: 0010:ida_free+0x134/0x140
> > > > Call Trace:
> > > >    <TASK>
> > > >    erofs_kill_sb+0x81/0x90
> > > >    deactivate_locked_super+0x35/0x80
> > > >    get_tree_bdev+0x136/0x1e0
> > > >    vfs_get_tree+0x2c/0xf0
> > > >    do_new_mount+0x190/0x2f0
> > > >    [...]
> > > > ============================================
> > > >
> > > > Now when erofs_kill_sb() is called, erofs_sb_info must have been
> > > > initialised, so use sbi->fsid to distinguish between the two modes.
> > > >
> > > > The Linux kernel CVE team has assigned CVE-2024-36966 to this issue.
> > > >
> > > >
> > > > Affected and fixed versions
> > > > ===========================
> > > >
> > > >      Fixed in 6.6.32 with commit f9b877a7ee31
> > > >      Fixed in 6.8.11 with commit dcdd49701e42
> > > >      Fixed in 6.9 with commit 7af2ae1b1531
> > > For reference, this issue doesn't affect Linux kernel below 6.6.
> > >
> > > This behavior ("s_bdev may not be initialized in erofs_kill_sb()")
> > > is introduced due to commit aca740cecbe5 ("fs: open block device after
> > > superblock creation").
> > >
> > > In other words, previously .kill_sb() was called only after
> > > fill_super failed and problematic erofs_kill_sb() called due to
> > > setup_bdev_super() failure can only happen since Linux 6.6.
> > >
> > > Thanks,
> > > Gao Xiang
> > Exactly! I'm so sorry I forgot to add the Fixes tag.
> No worries.  I've updated the CVE database with this information and the
> json file and web site will show the new information soon when it gets
> propagated.
>
> thanks,
>
> greg k-h

Thank you very much for the update!

--
With Best Regards,
Baokun Li