On Fri, 2020-01-31 at 12:20 +0000, Al Viro wrote:
On Fri, Jan 31, 2020 at 10:08:37AM +0000, Rantala, Tommi T. (Nokia - FI/Espoo) wrote:
On Tue, 2020-01-28 at 15:08 +0100, Greg Kroah-Hartman wrote:
From: Al Viro viro@zeniv.linux.org.uk
@@ -3258,6 +3259,8 @@ 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;
I hit the following oops in 4.19.100 while running kselftests.
fs/namei.c:3262 matches the line above.
Any ideas?
Yes. Make those two line kuid_t dir_uid = nd->inode->i_uid; umode_t dir_mode = nd->inode->i_mode;
I'm pretty sure that I know which way I'd fucked up there; we can get here in RCU mode with stale nd->path.dentry (that would make the thing fail with -ECHILD. with retry in non-RCU mode). In non-stale case nd->inode is the same as nd->path.dentry->d_inode and it's always pointing to a struct inode that hadn't been freed yet.
The oops does not seem to reproduce easily with kselftests, I've only hit it once with 4.19.100.
Made the change in fs/namei.c, so far no ill effects. I'll continue running the kselftests...
-Tommi