[PATCH] Re: KASAN: use-after-free Read in path_init (2)

Al Viro
2020-08-12T04:15:36Z

On Tue, Aug 11, 2020 at 08:17:16PM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 5631c5e0 Merge tag 'xfs-5.9-merge-7' of git://git.kernel.o..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17076984900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=afba7c06f91e56eb
> dashboard link: https://syzkaller.appspot.com/bug?extid=bbeb1c88016c7db4aa24
> compiler: gcc (GCC) 10.1.0-syz 20200507
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1502ce02900000

fix breakage in do_rmdir()

putname() should happen only after we'd *not* branched to
retry, same as it's done in do_unlinkat().

Fixes: e24ab0ef689d "fs: push the getname from do_rmdir into the callers"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/fs/namei.c b/fs/namei.c
index fde8fe086c09..9fa10c614de7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3770,11 +3770,11 @@ long do_rmdir(int dfd, struct filename *name)
mnt_drop_write(path.mnt);
exit1:
path_put(&path);
- putname(name);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;
goto retry;
}
+ putname(name);
return error;
}