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vfs: fix BUG_ON() in fs/namei.c:1461

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When Al moved the nameidata_dentry_drop_rcu_maybe() call into the
do_follow_link function in commit 844a391799 ("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>
This commit is contained in:
Linus Torvalds 2011-02-16 08:56:55 -08:00
parent 85e2efbb1d
commit 3abb17e82f
1 changed files with 4 additions and 5 deletions
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9
fs/namei.c
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@ -795,7 +795,7 @@ __do_follow_link(const struct path *link, struct nameidata *nd, void **p)
* 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 @@ static inline int do_follow_link(struct path *path, struct nameidata *nd)
/* 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 @@ exec_again:
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 @@ last_component:
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;