[PATCH] Fix double decrement of mqueue_mnt->mnt_count in sys_mq_open

Fixed the refcounting on failure exits in sys_mq_open() and
cleaned the logics up.  Rules are actually pretty simple - dentry_open()
expects vfsmount and dentry to be pinned down and it either transfers
them into created struct file or drops them.  Old code had been very
confused in that area - if dentry_open() had failed either in do_open()
or do_create(), we ended up dentry and mqueue_mnt dropped twice, once
by dentry_open() cleanup and then by sys_mq_open().

Fix consists of making the rules for do_create() and do_open()
same as for dentry_open() and updating the sys_mq_open() accordingly;
that actually leads to more straightforward code and less work on
normal path.

Signed-off-by: Al Viro <aviro@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 33 insertions, 26 deletions

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 4e776f9c80e7..59302fc3643b 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -599,15 +599,16 @@ static int mq_attr_ok(struct mq_attr *attr)
 static struct file *do_create(struct dentry *dir, struct dentry *dentry,
                         int oflag, mode_t mode, struct mq_attr __user *u_attr)
 {
-        struct file *filp;
         struct mq_attr attr;
         int ret;
 
-        if (u_attr != NULL) {
+        if (u_attr) {
+                ret = -EFAULT;
                 if (copy_from_user(&attr, u_attr, sizeof(attr)))
-                        return ERR_PTR(-EFAULT);
+                        goto out;
+                ret = -EINVAL;
                 if (!mq_attr_ok(&attr))
-                        return ERR_PTR(-EINVAL);
+                        goto out;
                 /* store for use during create */
                 dentry->d_fsdata = &attr;
         }
@@ -616,13 +617,14 @@ static struct file *do_create(struct dentry *dir, struct dentry *dentry,
         ret = vfs_create(dir->d_inode, dentry, mode, NULL);
         dentry->d_fsdata = NULL;
         if (ret)
-                return ERR_PTR(ret);
+                goto out;
 
-        filp = dentry_open(dentry, mqueue_mnt, oflag);
-        if (!IS_ERR(filp))
-                dget(dentry);
+        return dentry_open(dentry, mqueue_mnt, oflag);
 
-        return filp;
+out:
+        dput(dentry);
+        mntput(mqueue_mnt);
+        return ERR_PTR(ret);
 }
 
 /* Opens existing queue */
@@ -630,20 +632,20 @@ static struct file *do_open(struct dentry *dentry, int oflag)
 {
 static int oflag2acc[O_ACCMODE] = { MAY_READ, MAY_WRITE,
                                         MAY_READ | MAY_WRITE };
-        struct file *filp;
 
-        if ((oflag & O_ACCMODE) == (O_RDWR | O_WRONLY))
+        if ((oflag & O_ACCMODE) == (O_RDWR | O_WRONLY)) {
+                dput(dentry);
+                mntput(mqueue_mnt);
                 return ERR_PTR(-EINVAL);
+        }
 
-        if (permission(dentry->d_inode, oflag2acc[oflag & O_ACCMODE], NULL))
+        if (permission(dentry->d_inode, oflag2acc[oflag & O_ACCMODE], NULL)) {
+                dput(dentry);
+                mntput(mqueue_mnt);
                 return ERR_PTR(-EACCES);
+        }
 
-        filp = dentry_open(dentry, mqueue_mnt, oflag);
-
-        if (!IS_ERR(filp))
-                dget(dentry);
-
-        return filp;
+        return dentry_open(dentry, mqueue_mnt, oflag);
 }
 
 asmlinkage long sys_mq_open(const char __user *u_name, int oflag, mode_t mode,
@@ -671,17 +673,20 @@ asmlinkage long sys_mq_open(const char __user *u_name, int oflag, mode_t mode,
 
         if (oflag & O_CREAT) {
                 if (dentry->d_inode) {  /* entry already exists */
-                        filp = (oflag & O_EXCL) ? ERR_PTR(-EEXIST) :
-                                        do_open(dentry, oflag);
+                        error = -EEXIST;
+                        if (oflag & O_EXCL)
+                                goto out;
+                        filp = do_open(dentry, oflag);
                 } else {
                         filp = do_create(mqueue_mnt->mnt_root, dentry,
                                                 oflag, mode, u_attr);
                 }
-        } else
-                filp = (dentry->d_inode) ? do_open(dentry, oflag) :
-                                        ERR_PTR(-ENOENT);
-
-        dput(dentry);
+        } else {
+                error = -ENOENT;
+                if (!dentry->d_inode)
+                        goto out;
+                filp = do_open(dentry, oflag);
+        }
 
         if (IS_ERR(filp)) {
                 error = PTR_ERR(filp);
@@ -692,8 +697,10 @@ asmlinkage long sys_mq_open(const char __user *u_name, int oflag, mode_t mode,
         fd_install(fd, filp);
         goto out_upsem;
 
-out_putfd:
+out:
+        dput(dentry);
         mntput(mqueue_mnt);
+out_putfd:
         put_unused_fd(fd);
 out_err:
         fd = error;