Messages in this thread Patch in this message | | | From | "Rantala, Tommi T. (Nokia - FI/Espoo)" <> | Subject | Re: [PATCH 4.19 43/92] do_last(): fetch directory ->i_mode and ->i_uid before its too late | Date | Fri, 31 Jan 2020 13:57:46 +0000 |
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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
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