Make sure nd->path.mnt and nd->path.dentry are always valid pointers
Initialize them in set_nameidata() and make sure that terminate_walk() clears them
once the pointers become potentially invalid (i.e. we leave RCU mode or drop them
in non-RCU one). Currently we have "path_init() always initializes them and nobody
accesses them outside of path_init()/terminate_walk() segments", which is asking
for trouble.
With that change we would have nd->path.{mnt,dentry}
1) always valid - NULL or pointing to currently allocated objects.
2) non-NULL while we are successfully walking
3) NULL when we are not walking at all
4) contributing to refcounts whenever non-NULL outside of RCU mode.
Fixes: 6c6ec2b0a3e0 ("fs: add support for LOOKUP_CACHED")
Reported-by: syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com
Tested-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index 216f16e..fc8760d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -579,6 +579,8 @@
p->stack = p->internal;
p->dfd = dfd;
p->name = name;
+ p->path.mnt = NULL;
+ p->path.dentry = NULL;
p->total_link_count = old ? old->total_link_count : 0;
p->saved = old;
current->nameidata = p;
@@ -652,6 +654,8 @@
rcu_read_unlock();
}
nd->depth = 0;
+ nd->path.mnt = NULL;
+ nd->path.dentry = NULL;
}
/* path_put is needed afterwards regardless of success or failure */
@@ -2322,8 +2326,6 @@
}
nd->root.mnt = NULL;
- nd->path.mnt = NULL;
- nd->path.dentry = NULL;
/* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */
if (*s == '/' && !(flags & LOOKUP_IN_ROOT)) {
