vfs: Add a mount flag to lock read only bind mounts (90563b19) · Commits · e / devices / android_kernel_fairphone_FP4

When a read-only bind mount is copied from mount namespace in a higher privileged user namespace to a mount namespace in a lesser privileged user namespace, it should not be possible to remove the the read-only restriction. Add a MNT_LOCK_READONLY mount flag to indicate that a mount must remain read-only. CC: stable@vger.kernel.org Acked-by:

Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by:

"Eric W. Biederman" <ebiederm@xmission.com>

fs/namespace.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1713,6 +1713,9 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
		if (readonly_request == __mnt_is_readonly(mnt))
		return 0;

		if (mnt->mnt_flags & MNT_LOCK_READONLY)
		return -EPERM;

		if (readonly_request)
		error = mnt_make_readonly(real_mount(mnt));
		else

include/linux/mount.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -47,6 +47,8 @@ struct mnt_namespace;

		#define MNT_INTERNAL 0x4000

		#define MNT_LOCK_READONLY 0x400000

		struct vfsmount {
		struct dentry mnt_root; / root of the mounted tree */
		struct super_block mnt_sb; / pointer to superblock */