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Subject[PATCH 2/2] vfs: Fix refcnt leak with __do_follow_link() in do_filp_open()
Date
Hi,

I noticed refcnt leak in do_filp_open() by recent change. Could you
review this one?


__do_follow_link() handles "nd->path and path" refcnt by special way.
If path->mnt == nd->path.mnt (i.e. those is sharing the refcnt), it
gets refcnt of path->mnt, to make simple error path of it.

So, we can't call __do_follow_link() twice without special care,
because it will get refcnt of path->mnt twice. (i.e. current
do_filp_open() is leaking path->mnt if first __do_follow_link()
returned -ESTALE and path->mnt != nd->path.mnt)

This moves the special refcnt handling from __do_follow_link() as
path_unshare_refcnt(). Then call it once for that do_filp_open() path.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---

fs/namei.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff -puN fs/namei.c~namei-do_filp_open-fix fs/namei.c
--- linux-2.6/fs/namei.c~namei-do_filp_open-fix 2010-01-12 00:15:08.000000000 +0900
+++ linux-2.6-hirofumi/fs/namei.c 2010-01-12 00:15:08.000000000 +0900
@@ -548,6 +548,18 @@ static inline void path_to_nameidata(str
nd->path.dentry = path->dentry;
}

+/* NOTE: this is intended as special operation for __do_follow_link() */
+static inline void path_unshare_refcnt(struct path *path, struct nameidata *nd)
+{
+ if (path->mnt == nd->path.mnt)
+ mntget(path->mnt);
+}
+
+/*
+ * The caller should take special care about path and nd->path
+ * reference count. (e.g. to make simple error path, call
+ * path_unshare_refcnt() before this, etc.)
+ */
static __always_inline int __do_follow_link(struct path *path, struct nameidata *nd)
{
int error;
@@ -559,9 +571,8 @@ static __always_inline int __do_follow_l

if (path->mnt != nd->path.mnt) {
path_to_nameidata(path, nd);
- dget(dentry);
+ path_get(path);
}
- mntget(path->mnt);
cookie = dentry->d_inode->i_op->follow_link(dentry, nd);
error = PTR_ERR(cookie);
if (!IS_ERR(cookie)) {
@@ -602,6 +613,7 @@ static inline int do_follow_link(struct
current->link_count++;
current->total_link_count++;
nd->depth++;
+ path_unshare_refcnt(path, nd);
err = __do_follow_link(path, nd);
path_put(path);
current->link_count--;
@@ -1856,6 +1868,7 @@ do_link:
goto exit_dput;
save = nd.path;
path_get(&save);
+ path_unshare_refcnt(&path, &nd);
error = __do_follow_link(&path, &nd);
if (error == -ESTALE) {
/* nd.path had been dropped */
_
--
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>


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