umount: Allow superblock owners to force umount

Loosen the permission check on forced umount to allow users holding CAP_SYS_ADMIN privileges in namespaces that are privileged with respect to the userns that originally mounted the filesystem.

Trond Myklebust committed 1 year ago

Commit e1ff7aa1 parent e1c24b51 file · +2 −1Browse files

Unified · Split

fs/namespace.c+2−1

@@ -2105,6 +2105,7 @@ static void warn_mandlock(void) · 2104 unmodified lines
2105	2105	static int can_umount(const struct path *path, int flags)
2106	2106	{
2107	2107	struct mount *mnt = real_mount(path->mnt);
	2108	+ struct super_block *sb = path->dentry->d_sb;
2108	2109
2109	2110	if (!may_mount())
2110	2111	return -EPERM;
@@ -2114,7 +2115,7 @@ static int can_umount(const struct path *path, int flags) · 3 unmodified lines
2114	2115	return -EINVAL;
2115	2116	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
2116	2117	return -EINVAL;
2117		− if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
	2118	+ if (flags & MNT_FORCE && !ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
2118	2119	return -EPERM;
2119	2120	return 0;
2120	2121	}