From 3cdf6fe91041b3afd6761f76254f7b6cbe8020fc Mon Sep 17 00:00:00 2001 From: Seunghun Lee Date: Sat, 3 Jan 2015 02:26:49 +0900 Subject: ovl: Prevent rw remount when it should be ro mount Overlayfs should be mounted read-only when upper-fs is read-only or nonexistent. But now it can be remounted read-write and this can cause kernel panic. So we should prevent read-write remount when the above situation happens. Signed-off-by: Seunghun Lee Signed-off-by: Miklos Szeredi --- fs/overlayfs/super.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 9e94f4acef1a..b90952f528b1 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -525,10 +525,22 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry) return 0; } +static int ovl_remount(struct super_block *sb, int *flags, char *data) +{ + struct ovl_fs *ufs = sb->s_fs_info; + + if (!(*flags & MS_RDONLY) && + (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))) + return -EROFS; + + return 0; +} + static const struct super_operations ovl_super_operations = { .put_super = ovl_put_super, .statfs = ovl_statfs, .show_options = ovl_show_options, + .remount_fs = ovl_remount, }; enum { -- cgit v1.2.3