Re: general protection fault in path_openat

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, Jan 31, 2020 at 08:48:11PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    ccaaaf6f Merge tag 'mpx-for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=115bda4ee00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=879390c6b09ccf66
> dashboard link: https://syzkaller.appspot.com/bug?extid=190005201ced78a74ad6
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1674c776e00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1565e101e00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com

Already reported; see if the following fixes that:

diff --git a/fs/namei.c b/fs/namei.c
index 4167109297e0..db6565c99825 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3333,8 +3333,8 @@ static int do_last(struct nameidata *nd,
 		   struct file *file, const struct open_flags *op)
 {
 	struct dentry *dir = nd->path.dentry;
-	kuid_t dir_uid = dir->d_inode->i_uid;
-	umode_t dir_mode = dir->d_inode->i_mode;
+	kuid_t dir_uid = nd->inode->i_uid;
+	umode_t dir_mode = nd->inode->i_mode;
 	int open_flag = op->open_flag;
 	bool will_truncate = (open_flag & O_TRUNC) != 0;
 	bool got_write = false;