Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull namespace updates from Eric Biederman:
 "After a lot of discussion and work we have finally reachanged a basic
  understanding of what is necessary to make unprivileged mounts safe in
  the presence of EVM and IMA xattrs which the last commit in this
  series reflects. While technically it is a revert the comments it adds
  are important for people not getting confused in the future. Clearing
  up that confusion allows us to seriously work on unprivileged mounts
  of fuse in the next development cycle.

  The rest of the fixes in this set are in the intersection of user
  namespaces, ptrace, and exec. I started with the first fix which
  started a feedback cycle of finding additional issues during review
  and fixing them. Culiminating in a fix for a bug that has been present
  since at least Linux v1.0.

  Potentially these fixes were candidates for being merged during the rc
  cycle, and are certainly backport candidates but enough little things
  turned up during review and testing that I decided they should be
  handled as part of the normal development process just to be certain
  there were not any great surprises when it came time to backport some
  of these fixes"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  Revert "evm: Translate user/group ids relative to s_user_ns when computing HMAC"
  exec: Ensure mm->user_ns contains the execed files
  ptrace: Don't allow accessing an undumpable mm
  ptrace: Capture the ptracer's creds not PT_PTRACE_CAP
  mm: Add a user_ns owner to mm_struct and fix ptrace permission checks

1 files changed, 10 insertions, 2 deletions

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index bf663915412e..d7f282d75cc1 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -151,8 +151,16 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
 	memset(&hmac_misc, 0, sizeof(hmac_misc));
 	hmac_misc.ino = inode->i_ino;
 	hmac_misc.generation = inode->i_generation;
-	hmac_misc.uid = from_kuid(inode->i_sb->s_user_ns, inode->i_uid);
-	hmac_misc.gid = from_kgid(inode->i_sb->s_user_ns, inode->i_gid);
+	/* The hmac uid and gid must be encoded in the initial user
+	 * namespace (not the filesystems user namespace) as encoding
+	 * them in the filesystems user namespace allows an attack
+	 * where first they are written in an unprivileged fuse mount
+	 * of a filesystem and then the system is tricked to mount the
+	 * filesystem for real on next boot and trust it because
+	 * everything is signed.
+	 */
+	hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
+	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
 	hmac_misc.mode = inode->i_mode;
 	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
 	if (evm_hmac_attrs & EVM_ATTR_FSUUID)