mount_subtree() pointless use-after-free
d'oh... we'd carefully pinned mnt->mnt_sb down, dropped mnt and attempt
to grab s_umount on mnt->mnt_sb. The trouble is, *mnt might've been
overwritten by now...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index 50ee303..6d3a196 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2493,6 +2493,7 @@
struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
{
struct mnt_namespace *ns;
+ struct super_block *s;
struct path path;
int err;
@@ -2509,10 +2510,11 @@
return ERR_PTR(err);
/* trade a vfsmount reference for active sb one */
- atomic_inc(&path.mnt->mnt_sb->s_active);
+ s = path.mnt->mnt_sb;
+ atomic_inc(&s->s_active);
mntput(path.mnt);
/* lock the sucker */
- down_write(&path.mnt->mnt_sb->s_umount);
+ down_write(&s->s_umount);
/* ... and return the root of (sub)tree on it */
return path.dentry;
}