Re: [PATCH] reiserfs: fix race in readdir

[Jan Kara <jack@suse.cz>]

On Wed 02-04-14 20:09:55, Jan Kara wrote:
> On Wed 02-04-14 11:57:54, Jeff Mahoney wrote:
> > jdm-20004 reiserfs_delete_xattrs: Couldn't delete all xattrs (-2)
> > 
> > The -ENOENT is due to readdir calling dir_emit on the same entry twice.
> > 
> > If the dir_emit callback sleeps and the tree is changed underneath us,
> > we won't be able to trust deh_offset(deh) anymore. We need to save
> > next_pos before we might sleep so we can find the next entry.
> > 
> > This can also affect non-xattr users of readdir, though the race is tighter.
> > 
> > Cc: <stable@vger.kernel.org> 
> > Signed-off-by: Jeff Mahoney <jeffm@suse.com>
>   The patch looks good to me so unless someone objects, I'll merge this
> patch with Linus.
  Umm, actually, what if dir_emit() returns error? Previously we tried
again the same entry, now we continue with the next one. Is that intended?
If yes, please comment on that in the changelog.

								Honza


> > ---
> >  fs/reiserfs/dir.c |    9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > --- a/fs/reiserfs/dir.c
> > +++ b/fs/reiserfs/dir.c
> > @@ -179,6 +179,13 @@ int reiserfs_readdir_inode(struct inode
> >  				memcpy(local_buf, d_name, d_reclen);
> >  
> >  				/*
> > +				 * deh_offset(deh) will be invalid if dir_emit
> > +				 * sleeps. We need to know the offset after
> > +				 * this one to continue.
> > +				 */
> > +				next_pos = deh_offset(deh) + 1;
> > +
> > +				/*
> >  				 * Since filldir might sleep, we can release
> >  				 * the write lock here for other waiters
> >  				 */
> > @@ -196,8 +203,6 @@ int reiserfs_readdir_inode(struct inode
> >  				if (local_buf != small_buf) {
> >  					kfree(local_buf);
> >  				}
> > -				// next entry should be looked for with such offset
> > -				next_pos = deh_offset(deh) + 1;
> >  
> >  				if (item_moved(&tmp_ih, &path_to_entry)) {
> >  					set_cpu_key_k_offset(&pos_key,
> > 
> > -- 
> > Jeff Mahoney
> > SUSE Labs
> -- 
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR