[PATCH] spufs: check for proper file pointer in sys_spu_run

Only checking for SPUFS_MAGIC is not reliable, because
it might not be unique in theory. Worse than that,
we accidentally allow spu_run to be performed on
any file in spufs, not just those returned from
spu_create as intended.

Noticed by Al Viro.
Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/cell/spufs/inode.c

@@ -212,7 +212,7 @@ struct inode_operations spufs_dir_inode_operations = {
 	.lookup = simple_lookup,
 };
 
-struct file_operations spufs_autodelete_dir_operations = {
+struct file_operations spufs_context_fops = {
 	.open		= dcache_dir_open,
 	.release	= spufs_dir_close,
 	.llseek		= dcache_dir_lseek,
@@ -301,7 +301,7 @@ spufs_create_thread(struct nameidata *nd, const char *name,
 		put_unused_fd(ret);
 		ret = PTR_ERR(filp);
 	} else {
-		filp->f_op = &spufs_autodelete_dir_operations;
+		filp->f_op = &spufs_context_fops;
 		fd_install(ret, filp);
 	}
 

arch/powerpc/platforms/cell/spufs/spufs.h

@@ -103,6 +103,7 @@ long spufs_run_spu(struct file *file,
 		   struct spu_context *ctx, u32 *npc, u32 *status);
 long spufs_create_thread(struct nameidata *nd, const char *name,
 			 unsigned int flags, mode_t mode);
+extern struct file_operations spufs_context_fops;
 
 /* context management */
 struct spu_context * alloc_spu_context(struct address_space *local_store);

arch/powerpc/platforms/cell/spufs/syscalls.c

@@ -39,8 +39,9 @@ long do_spu_run(struct file *filp, __u32 __user *unpc, __u32 __user *ustatus)
 	if (get_user(npc, unpc) || get_user(status, ustatus))
 		goto out;
 
+	/* check if this file was created by spu_create */
 	ret = -EINVAL;
-	if (filp->f_vfsmnt->mnt_sb->s_magic != SPUFS_MAGIC)
+	if (filp->f_op != &spufs_context_fops)
 		goto out;
 
 	i = SPUFS_I(filp->f_dentry->d_inode);