Commit 7d01ef75 authored by Al Viro's avatar Al Viro
Browse files

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: 6c6ec2b0 ("fs: add support for LOOKUP_CACHED")
Reported-by: default avatar <syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com>
Tested-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 7f6c411c

fs/namei.c

+4 −2
Original line number Diff line number Diff line
@@ -579,6 +579,8 @@ static void set_nameidata(struct nameidata *p, int dfd, struct filename *name) 
	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 @@ static void terminate_walk(struct nameidata *nd) 
		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 @@ static const char *path_init(struct nameidata *nd, unsigned flags) 
	}



	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)) {