fix execute checking in permission()

permission() checks that MAY_EXEC is only allowed on regular files if at least
one execute bit is set in the file mode.

generic_permission() already ensures this, so the extra check in permission()
is superfluous.

If the filesystem defines it's own ->permission() the check may still be
needed.  In this case move it after ->permission().  This is needed because
filesystems such as FUSE may need to refresh the inode attributes before
checking permissions.

This check should be moved inside ->permission(), but that's another story.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 12 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 7cba63295a82..2792e0ca01d4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -227,10 +227,10 @@ int generic_permission(struct inode *inode, int mask,
 
 int permission(struct inode *inode, int mask, struct nameidata *nd)
 {
-        umode_t mode = inode->i_mode;
         int retval, submask;
 
         if (mask & MAY_WRITE) {
+                umode_t mode = inode->i_mode;
 
                 /*
                  * Nobody gets write access to a read-only fs.
@@ -246,22 +246,34 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
                         return -EACCES;
         }
 
-
-        /*
-         * MAY_EXEC on regular files requires special handling: We override
-         * filesystem execute permissions if the mode bits aren't set or
-         * the fs is mounted with the "noexec" flag.
-         */
-        if ((mask & MAY_EXEC) && S_ISREG(mode) && (!(mode & S_IXUGO) ||
-                        (nd && nd->mnt && (nd->mnt->mnt_flags & MNT_NOEXEC))))
-                return -EACCES;
+        if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode)) {
+                /*
+                 * MAY_EXEC on regular files is denied if the fs is mounted
+                 * with the "noexec" flag.
+                 */
+                if (nd && nd->mnt && (nd->mnt->mnt_flags & MNT_NOEXEC))
+                        return -EACCES;
+        }
 
         /* Ordinary permission routines do not understand MAY_APPEND. */
         submask = mask & ~MAY_APPEND;
-        if (inode->i_op && inode->i_op->permission)
+        if (inode->i_op && inode->i_op->permission) {
                 retval = inode->i_op->permission(inode, submask, nd);
-        else
+                if (!retval) {
+                        /*
+                         * Exec permission on a regular file is denied if none
+                         * of the execute bits are set.
+                         *
+                         * This check should be done by the ->permission()
+                         * method.
+                         */
+                        if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode) &&
+                            !(inode->i_mode & S_IXUGO))
+                                return -EACCES;
+                }
+        } else {
                 retval = generic_permission(inode, submask, NULL);
+        }
         if (retval)
                 return retval;