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fs: Allow superblock owner to access do_remount_sb()

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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.com>
Acked-by: Christian Brauner <christian@brauner.io>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-09-18 17:58:08 -05:00
parent 0031181c49
commit bc6155d132
1 changed files with 2 additions and 2 deletions
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4
fs/namespace.c
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@ -1590,7 +1590,7 @@ static int do_umount(struct mount *mnt, int flags)
* Special case for "unmounting" root ... * Special case for "unmounting" root ...
* we just try to remount it readonly. * we just try to remount it readonly.
*/ */
if (!capable(CAP_SYS_ADMIN)) if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
return -EPERM; return -EPERM;
down_write(&sb->s_umount); down_write(&sb->s_umount);
if (!sb_rdonly(sb)) if (!sb_rdonly(sb))
@ -2333,7 +2333,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
down_write(&sb->s_umount); down_write(&sb->s_umount);
if (ms_flags & MS_BIND) if (ms_flags & MS_BIND)
err = change_mount_flags(path->mnt, ms_flags); err = change_mount_flags(path->mnt, ms_flags);
else if (!capable(CAP_SYS_ADMIN)) else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
err = -EPERM; err = -EPERM;
else else
err = do_remount_sb(sb, sb_flags, data, 0); err = do_remount_sb(sb, sb_flags, data, 0);