Re: [PATCH][udf-next] udf: don't call mark_buffer_dirty on a null bh pointer

[Steve Magnani]

On 2/19/19 8:02 AM, Jan Kara wrote:
> On Tue 19-02-19 11:44:03, Colin King wrote:
> > From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> >
> > There is a null check on the pointer bh to avoid a null pointer dereference
> > on bh->b_data however later bh is passed to mark_buffer_dirty that can also
> > cause a null pointer dereference on bh.  Avoid this potential null pointer
> > dereference by moving the call to mark_buffer_dirty inside the null checked
> > block.
> >
> > Fixes: e8b4274735e4 ("udf: finalize integrity descriptor before writeback")
> > Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Thanks for the patch! In fact it is the 'if (bh)' check that's
> unnecessarily defensive (we cannot have sbi->s_lvid_dirty and
> !sbi->s_lvid_bh). So I'll just drop that check (attached patch).
>
> 								Honza
>
> > ---
> >   fs/udf/super.c | 12 ++++++------
> >   1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/udf/super.c b/fs/udf/super.c
> > index a6940d90bedd..b7e9a83d39db 100644
> > --- a/fs/udf/super.c
> > +++ b/fs/udf/super.c
> > @@ -2336,13 +2336,13 @@ static int udf_sync_fs(struct super_block *sb, int wait)
> >   
> >   			lvid = (struct logicalVolIntegrityDesc *)bh->b_data;
> >   			udf_finalize_lvid(lvid);
> > -		}
> >   
> > -		/*
> > -		 * Blockdevice will be synced later so we don't have to submit
> > -		 * the buffer for IO
> > -		 */
> > -		mark_buffer_dirty(bh);
> > +			/*
> > +			 * Blockdevice will be synced later so we don't have
> > +			 * to submit the buffer for IO
> > +			 */
> > +			mark_buffer_dirty(bh);
> > +		}
> >   		sbi->s_lvid_dirty = 0;
> >   	}
> >   	mutex_unlock(&sbi->s_alloc_mutex);
> > --
> > 2.20.1
Reviewed-by: Steven J. Magnani <steve@xxxxxxxxxxxxxxx>

Doh! Thanks for the catch Colin.

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