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Subject[PATCH v3 16/21] fs: Allow superblock owner to access do_remount_sb()
Date
Superblock level remounts are currently restricted to global
CAP_SYS_ADMIN, as is the path for changing the root mount to
read only on umount. Loosen both of these permission checks to
also allow CAP_SYS_ADMIN in any namespace which is privileged
towards the userns which originally mounted the filesystem.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
---
fs/namespace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 0ad8e4a4f50b..575e3f8b34fd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1510,7 +1510,7 @@ static int do_umount(struct mount *mnt, int flags)
* Special case for "unmounting" root ...
* we just try to remount it readonly.
*/
- if (!capable(CAP_SYS_ADMIN))
+ if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
return -EPERM;
down_write(&sb->s_umount);
if (!(sb->s_flags & MS_RDONLY))
@@ -2207,7 +2207,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
down_write(&sb->s_umount);
if (flags & MS_BIND)
err = change_mount_flags(path->mnt, flags);
- else if (!capable(CAP_SYS_ADMIN))
+ else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
err = -EPERM;
else
err = do_remount_sb(sb, flags, data, 0);
--
1.9.1
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