On Thu 01-10-20 14:35:47, Anmol Karn wrote: > d_really_is_negative() checks for the dentry->d_inode whether it's NULL > or not, but in open_xa_root(), when it checks 'privroot->d_inode', it > doesn't check whether privroot is NULL or not, this leads to a null > pointer dereference while calling it from open_xa_dir() while > initializing xaroot. > > - fs/reiserfs/xattr.c > The bug seems to get triggered at this line: > > if (d_really_is_negative(privroot)) > return ERR_PTR(-EOPNOTSUPP); > > Fix it by adding a NULL check for privroot. > > Reported-and-tested-by: syzbot+9b33c9b118d77ff59b6f@xxxxxxxxxxxxxxxxxxxxxxxxx > Link: https://syzkaller.appspot.com/bug?extid=9b33c9b118d77ff59b6f > Signed-off-by: Anmol Karn <anmol.karan123@xxxxxxxxx> Thanks for the patch! I've already fixed the problem myself (slightly differently) but I'll comment about your patch below for educational purposes :). See https://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git/commit/?h=for_next&id=c2bb80b8bdd04dfe32364b78b61b6a47f717af52 > diff --git a/fs/reiserfs/xattr.c b/fs/reiserfs/xattr.c > index 28b241cd6987..a75480d0ee7e 100644 > --- a/fs/reiserfs/xattr.c > +++ b/fs/reiserfs/xattr.c > @@ -121,8 +121,9 @@ static struct dentry *open_xa_root(struct super_block *sb, int flags) > struct dentry *privroot = REISERFS_SB(sb)->priv_root; > struct dentry *xaroot; > > - if (d_really_is_negative(privroot)) > + if (!privroot || d_really_is_negative(privroot)) { > return ERR_PTR(-EOPNOTSUPP); I don't think EOPNOTSUPP is correct return code for !privroot case. AFAICS it would propagate out of reiserfs xattr code and would result in denying access to lookup_one_len() so xattr dir could never be initialized for such filesystem. So we need to return 0 (success, no xattrs present) in this case and because this is just a special case when we are initializing xattr dir and recurse back into xattr code, I've decided to perform this check directly in reiserfs_xattr_get(). > + } There's no need for additional braces in this 'if'. > > inode_lock_nested(d_inode(privroot), I_MUTEX_XATTR); Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
