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

[Greg Kroah-Hartman]

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