Re: general protection fault in getname_kernel

[Al Viro]

On Sun, Oct 07, 2018 at 04:44:03PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    c1d84a1b42ef Merge git://git.kernel.org/pub/scm/linux/kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10f3c6a1400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c0af03fe452b65fb
> dashboard link: https://syzkaller.appspot.com/bug?extid=c54f8e94e6bba03b04e9
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10688159400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1162aa31400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+c54f8e94e6bba03b04e9@xxxxxxxxxxxxxxxxxxxxxxxxx

Umm...  See if this helps:
diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index c2469833b4fb..6b84ef6ccff3 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1333,6 +1333,9 @@ static struct dentry *gfs2_mount_meta(struct file_system_type *fs_type,
 	struct path path;
 	int error;
 
+	if (!dev_name || !*dev_name)
+		return ERR_PTR(-EINVAL);
+
 	error = kern_path(dev_name, LOOKUP_FOLLOW, &path);
 	if (error) {
 		pr_warn("path_lookup on %s returned error %d\n",