[PATCH] user_ns: Add support for unprivileged remount

[Zhao Hongjiang <zhaohongjiang37-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

From: Zhao Hongjiang <zhaohongjiang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>

Relax the permission checks to allow unprivileged users that have
CAP_SYS_ADMIN permissions in the user namespace referred to by the
current mount namespace to be allowed to remount filesystems.

Signed-off-by: Zhao Hongjiang <zhaohongjiang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
---
 fs/namespace.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index af238d0..72be266 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1748,7 +1748,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
 	struct super_block *sb = path->mnt->mnt_sb;
 	struct mount *mnt = real_mount(path->mnt);

-	if (!capable(CAP_SYS_ADMIN))
+	if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;

 	if (!check_mnt(mnt))
-- 1.7.1