vfs: fix BUG_ON() in fs/namei.c:1461
When Al moved the nameidata_dentry_drop_rcu_maybe() call into the
do_follow_link function in commit 844a391799c2 ("nothing in
do_follow_link() is going to see RCU"), he mistakenly left the
BUG_ON(inode != path->dentry->d_inode);
behind. Which would otherwise be ok, but that BUG_ON() really needs to
be _after_ dropping RCU, since the dentry isn't necessarily stable
otherwise.
So complete the code movement in that commit, and move the BUG_ON() into
do_follow_link() too. This means that we need to pass in 'inode' as an
argument (just for this one use), but that's a small thing. And
eventually we may be confident enough in our path lookup that we can
just remove the BUG_ON() and the unnecessary inode argument.
Reported-and-tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/namei.c b/fs/namei.c
index 9e701e2..0087cf9 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -795,7 +795,7 @@
* Without that kind of total limit, nasty chains of consecutive
* symlinks can cause almost arbitrarily long lookups.
*/
-static inline int do_follow_link(struct path *path, struct nameidata *nd)
+static inline int do_follow_link(struct inode *inode, struct path *path, struct nameidata *nd)
{
void *cookie;
int err = -ELOOP;
@@ -803,6 +803,7 @@
/* We drop rcu-walk here */
if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry))
return -ECHILD;
+ BUG_ON(inode != path->dentry->d_inode);
if (current->link_count >= MAX_NESTED_LINKS)
goto loop;
@@ -1413,8 +1414,7 @@
goto out_dput;
if (inode->i_op->follow_link) {
- BUG_ON(inode != next.dentry->d_inode);
- err = do_follow_link(&next, nd);
+ err = do_follow_link(inode, &next, nd);
if (err)
goto return_err;
nd->inode = nd->path.dentry->d_inode;
@@ -1458,8 +1458,7 @@
break;
if (inode && unlikely(inode->i_op->follow_link) &&
(lookup_flags & LOOKUP_FOLLOW)) {
- BUG_ON(inode != next.dentry->d_inode);
- err = do_follow_link(&next, nd);
+ err = do_follow_link(inode, &next, nd);
if (err)
goto return_err;
nd->inode = nd->path.dentry->d_inode;