vfs: canonicalize create mode in build_open_flags()

Userspace can pass weird create mode in open(2) that we canonicalize to 
"(mode & S_IALLUGO) | S_IFREG" in vfs_create().

The problem is that we use the uncanonicalized mode before calling vfs_create()
with unforseen consequences.

So do the canonicalization early in build_open_flags().

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
CC: stable@vger.kernel.org

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/open.c b/fs/open.c
index bc132e167d2d..e1f2cdb91a4d 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -852,9 +852,10 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o
         int lookup_flags = 0;
         int acc_mode;
 
-        if (!(flags & O_CREAT))
-                mode = 0;
-        op->mode = mode;
+        if (flags & O_CREAT)
+                op->mode = (mode & S_IALLUGO) | S_IFREG;
+        else
+                op->mode = 0;
 
         /* Must never be set by userspace */
         flags &= ~FMODE_NONOTIFY;