On Fri, Apr 18, 2014 at 03:48:37AM +0100, Al Viro wrote:
> Crap... No, it's a bit trickier - we start with clearing all flags,
> so if we see the _intermediate_ d_flags and new d_inode, we'll sail
> past the check. Which would leave us with correct inode, but might
> give us a false negative in should_follow_link().
Note that most of the places calling d_is_...() are protected by
the following: if we'd obtained dentry by __lookup_hash() and friends
*after* grabbing ->i_mutex on parent, we are fine - both positive-to-negative
and negative-to-positive are possible only with ->i_mutex held, so it
gives us a barrier.
AFAICS, there are two more tricky places: walk_component() doing
if (!inode)
goto out_path_put;
if (should_follow_link(path->dentry, follow)) {
with unpleasant consequences if the second test gives a false negative,
and similar for mountpoint_last().
Basically, we'd concentrated on RCU races back then, and missed the possibility
of non-RCU-but-without-i_mutex ones. Proposed fix follows:
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
diff --git a/fs/dcache.c b/fs/dcache.c
index 40707d8..494a9def 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1647,8 +1647,7 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
unsigned add_flags = d_flags_for_inode(inode);
spin_lock(&dentry->d_lock);
- dentry->d_flags &= ~DCACHE_ENTRY_TYPE;
- dentry->d_flags |= add_flags;
+ __d_set_type(dentry, add_flags);
if (inode)
hlist_add_head(&dentry->d_alias, &inode->i_dentry);
dentry->d_inode = inode;
diff --git a/fs/namei.c b/fs/namei.c
index c6157c8..8016827 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1542,7 +1542,7 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
inode = path->dentry->d_inode;
}
err = -ENOENT;
- if (!inode)
+ if (!inode || d_is_negative(path->dentry))
goto out_path_put;
if (should_follow_link(path->dentry, follow)) {
@@ -2249,7 +2249,7 @@ mountpoint_last(struct nameidata *nd, struct path *path)
mutex_unlock(&dir->d_inode->i_mutex);
done:
- if (!dentry->d_inode) {
+ if (!dentry->d_inode || d_is_negative(dentry)) {
error = -ENOENT;
dput(dentry);
goto out;
@@ -2994,7 +2994,7 @@ retry_lookup:
finish_lookup:
/* we _can_ be in RCU mode here */
error = -ENOENT;
- if (d_is_negative(path->dentry)) {
+ if (!inode || d_is_negative(path->dentry)) {
path_to_nameidata(path, nd);
goto out;
}
--
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