Re: [PATCH 5.10/5.15] jfs: add check if log->bdev is NULL in lbmStartIO()

[Greg Kroah-Hartman]

On Fri, Jan 12, 2024 at 08:31:30PM +0100, Greg Kroah-Hartman wrote:
> On Fri, Jan 12, 2024 at 07:50:07PM +0300, Mikhail Ukhin wrote:
> > Fuzzing of 5.10 stable branch shows NULL pointer dereference happens in 
> > lbmStartIO() on log->bdev pointer. The reason for bdev being NULL is the 
> > JFS_NOINTEGRITY flag is set on mount of this fs. When this flag is enabled,
> > it results in the open_dummy_log function being called, which initializes a
> > new dummy_log, but does not assign a value to bdev.
> > 
> > The error is fixed in 5.18 by commit
> > 07888c665b405b1cd3577ddebfeb74f4717a84c4.
> > Backport of this commit is too intrusive, so it is more reasonable to apply
> > a small patch to fix this issue.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with syzkaller.
> > 
> > Signed-off-by: Mikhail Ukhin <mish.uxin2012@xxxxxxxxx>
> > Signed-off-by: Mikhail Ivanov <iwanov-23@xxxxx>
> > Signed-off-by: Pavel Koshutin <koshutin.pavel@xxxxxxxxx>
> > Signed-off-by: Artem Sadovnikov <ancowi69@xxxxxxxxx>
> > ---
> >  fs/jfs/jfs_logmgr.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Who is using jfs in 5.10 and 5.15?  Why not just mark the filesystem as
> BROKEN there instead?  If you need to access your ancient filesystem
> image just use a newer kernel.
> 
> For filesystems that are not used in older kernels, work like this feels
> odd, especially for something just like a NULL dereference which doesn't
> do much, right?

Now dropped from my review queue due to lack of response...