[PATCH] reiserfs: update reiserfs_xattrs_initialized() condition

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

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@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 6cb4aff0a77cc0e6 ("reiserfs: fix oops while creating privroot with selinux enabled")
---
 fs/reiserfs/xattr.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Escalating from reiserfs-devel@vger.kernel.org to linux-fsdevel@vger.kernel.org , for
no response from reiserfs developers for one month. If still no response from fsdevel
people, I would have to directly send to Linus...

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