On Fri 05-03-21 15:31:26, Tetsuo Handa wrote:
> syzbot is reporting NULL pointer dereference at reiserfs_security_init()
> [1], for commit ab17c4f02156c4f7 ("reiserfs: fixup xattr_root caching") is
> assuming that REISERFS_SB(s)->xattr_root != NULL in
> reiserfs_xattr_jcreate_nblocks() despite that commit made
> REISERFS_SB(sb)->priv_root != NULL && REISERFS_SB(s)->xattr_root == NULL
> case possible.
>
> I guess that commit 6cb4aff0a77cc0e6 ("reiserfs: fix oops while creating
> privroot with selinux enabled") wanted to check xattr_root != NULL before
> reiserfs_xattr_jcreate_nblocks(), for the changelog is talking about the
> xattr root.
>
> The issue is that while creating the privroot during mount
> reiserfs_security_init calls reiserfs_xattr_jcreate_nblocks which
> dereferences the xattr root. The xattr root doesn't exist, so we get an
> oops.
>
> Therefore, update reiserfs_xattrs_initialized() to check both the privroot
> and the xattr root.
>
> [1] https://syzkaller.appspot.com/bug?id=8abaedbdeb32c861dc5340544284167dd0e46cde
>
> Reported-and-tested-by: syzbot <syzbot+690cb1e51970435f9775@xxxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Fixes: 6cb4aff0a77cc0e6 ("reiserfs: fix oops while creating privroot with selinux enabled")
Thanks for the patch Tetsuo! I'd prefer if Jeff had a look since he has
written this code back then. But let me provide my view: I agree that for a
corrupted filesystem it can happen that xattr_root remains NULL although
priv_root is set. So your change makes sense. But then
reiserfs_xattrs_initialized() seems to be used really minimally? Only once
in fs/reiserfs/xattr_security.c and e.g. reiserfs_xattr_set() is prone to
the same problem? Do I miss something?
Honza
> diff --git a/fs/reiserfs/xattr.h b/fs/reiserfs/xattr.h
> index c764352447ba..81bec2c80b25 100644
> --- a/fs/reiserfs/xattr.h
> +++ b/fs/reiserfs/xattr.h
> @@ -43,7 +43,7 @@ void reiserfs_security_free(struct reiserfs_security_handle *sec);
>
> static inline int reiserfs_xattrs_initialized(struct super_block *sb)
> {
> - return REISERFS_SB(sb)->priv_root != NULL;
> + return REISERFS_SB(sb)->priv_root && REISERFS_SB(sb)->xattr_root;
> }
>
> #define xattr_size(size) ((size) + sizeof(struct reiserfs_xattr_header))
> --
> 2.18.4
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
