Fix possible filp_cachep memory corruption

In commit 31e6b01f4183 ("fs: rcu-walk for path lookup") we started doing
path lookup using RCU, which then falls back to a careful non-RCU lookup
in case of problems (LOOKUP_REVAL).  So do_filp_open() has this "re-do
the lookup carefully" looping case.

However, that means that we must not release the open-intent file data
if we are going to loop around and use it once more!

Fix this by moving the release of the open-intent data to the function
that allocates it (do_filp_open() itself) rather than the helper
functions that can get called multiple times (finish_open() and
do_last()).  This makes the logic for the lifetime of that field much
more obvious, and avoids the possible double free.

Reported-by: J. R. Okajima <hooanon05@yahoo.co.jp>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 10 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 7d77f24d32a9..ec4b2d0190a8 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -561,10 +561,14 @@ static inline int nameidata_drop_rcu_last_maybe(struct nameidata *nd)
  */
 void release_open_intent(struct nameidata *nd)
 {
-        if (nd->intent.open.file->f_path.dentry == NULL)
-                put_filp(nd->intent.open.file);
-        else
-                fput(nd->intent.open.file);
+        struct file *file = nd->intent.open.file;
+
+        if (file && !IS_ERR(file)) {
+                if (file->f_path.dentry == NULL)
+                        put_filp(file);
+                else
+                        fput(file);
+        }
 }
 
 /*
@@ -2265,8 +2269,6 @@ static struct file *finish_open(struct nameidata *nd,
         return filp;
 
 exit:
-        if (!IS_ERR(nd->intent.open.file))
-                release_open_intent(nd);
         path_put(&nd->path);
         return ERR_PTR(error);
 }
@@ -2389,8 +2391,6 @@ exit_mutex_unlock:
 exit_dput:
         path_put_conditional(path, nd);
 exit:
-        if (!IS_ERR(nd->intent.open.file))
-                release_open_intent(nd);
         path_put(&nd->path);
         return ERR_PTR(error);
 }
@@ -2477,6 +2477,7 @@ struct file *do_filp_open(int dfd, const char *pathname,
         }
         audit_inode(pathname, nd.path.dentry);
         filp = finish_open(&nd, open_flag, acc_mode);
+        release_open_intent(&nd);
         return filp;
 
 creat:
@@ -2553,6 +2554,7 @@ out:
                 path_put(&nd.root);
         if (filp == ERR_PTR(-ESTALE) && !(flags & LOOKUP_REVAL))
                 goto reval;
+        release_open_intent(&nd);
         return filp;
 
 exit_dput:
@@ -2560,8 +2562,6 @@ exit_dput:
 out_path:
         path_put(&nd.path);
 out_filp:
-        if (!IS_ERR(nd.intent.open.file))
-                release_open_intent(&nd);
         filp = ERR_PTR(error);
         goto out;
 }
diff --git a/fs/open.c b/fs/open.c
index e52389e1f05b..5a2c6ebc22b5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -790,6 +790,8 @@ struct file *nameidata_to_filp(struct nameidata *nd)
 
         /* Pick up the filp from the open intent */
         filp = nd->intent.open.file;
+        nd->intent.open.file = NULL;
+
         /* Has the filesystem initialised the file for us? */
         if (filp->f_path.dentry == NULL) {
                 path_get(&nd->path);