[PATCH] userns: allow remount filesystem in un-init userns

[Gao feng]

The proc and sysfs filesystem already enable userns support,
remounting these filesystems in un-init userns do no harm
to the host.

Signed-off-by: Gao feng <gaofeng at cn.fujitsu.com>
---
 fs/namespace.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 55605c5..b9d83fb 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1748,7 +1748,10 @@ 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 (sb->s_type->fs_flags & FS_USERNS_MOUNT) {
+		if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))
+			return -EPERM;
+	} else if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
 	if (!check_mnt(mnt))
-- 
1.7.11.7


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