vfs: Add sb_rdonly(sb) to query the MS_RDONLY flag on s_flags

Add an sb_rdonly() function to query the MS_RDONLY flag on sb->s_flags
preparatory to providing an SB_RDONLY flag.

Signed-off-by: David Howells <dhowells@redhat.com>
(cherry picked from commit 94e92e7ac90d06e1e839e112d3ae80b2457dbdd7)

Orabug: 29428607
CVE: CVE-2018-10878

Signed-off-by: John Donnelly <John.P.Donnelly@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/include/linux/fs.h b/include/linux/fs.h
index f8fd2cdbd6fd0ceedac8259cb9998bb05fe95731..da484eb393c77ea33ba383e0ee0d285a788e9f92 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1754,7 +1754,8 @@ struct super_operations {
  */
 #define __IS_FLG(inode, flg)   ((inode)->i_sb->s_flags & (flg))
 
-#define IS_RDONLY(inode)       ((inode)->i_sb->s_flags & MS_RDONLY)
+static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags & MS_RDONLY; }
+#define IS_RDONLY(inode)       sb_rdonly((inode)->i_sb)
 #define IS_SYNC(inode)         (__IS_FLG(inode, MS_SYNCHRONOUS) || \
                                        ((inode)->i_flags & S_SYNC))
 #define IS_DIRSYNC(inode)      (__IS_FLG(inode, MS_SYNCHRONOUS|MS_DIRSYNC) || \