+ user_ns-use-correct-check-for-single-threadedness.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     Subject: user_ns: use correct check for single-threadedness
has been added to the -mm tree.  Its filename is
     user_ns-use-correct-check-for-single-threadedness.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/user_ns-use-correct-check-for-single-threadedness.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/user_ns-use-correct-check-for-single-threadedness.patch

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------------------------------------------------------
From: Ricky Zhou <rickyz@xxxxxxxxxxxx>
Subject: user_ns: use correct check for single-threadedness

Checking mm_users > 1 does not mean a process is multithreaded.  For
example, reading /proc/PID/maps temporarily increments mm_users, allowing
other processes to (accidentally) interfere with unshare() calls.

This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly
returning EINVAL if another processes happened to be simultaneously
reading the maps file.

Signed-off-by: Ricky Zhou <rickyz@xxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Julien Tinnes <jln@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>	[3.9+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/fork.c           |    4 ++--
 kernel/user_namespace.c |    3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff -puN kernel/fork.c~user_ns-use-correct-check-for-single-threadedness kernel/fork.c
--- a/kernel/fork.c~user_ns-use-correct-check-for-single-threadedness
+++ a/kernel/fork.c
@@ -75,6 +75,7 @@
 #include <linux/aio.h>
 #include <linux/compiler.h>
 #include <linux/sysctl.h>
+#include <linux/sched.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1876,8 +1877,7 @@ static int check_unshare_flags(unsigned
 	 * needs to unshare vm.
 	 */
 	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
-		/* FIXME: get_task_mm() increments ->mm_users */
-		if (atomic_read(&current->mm->mm_users) > 1)
+		if (!current_is_single_threaded())
 			return -EINVAL;
 	}
 
diff -puN kernel/user_namespace.c~user_ns-use-correct-check-for-single-threadedness kernel/user_namespace.c
--- a/kernel/user_namespace.c~user_ns-use-correct-check-for-single-threadedness
+++ a/kernel/user_namespace.c
@@ -22,6 +22,7 @@
 #include <linux/ctype.h>
 #include <linux/projid.h>
 #include <linux/fs_struct.h>
+#include <linux/sched.h>
 
 static struct kmem_cache *user_ns_cachep __read_mostly;
 static DEFINE_MUTEX(userns_state_mutex);
@@ -977,7 +978,7 @@ static int userns_install(struct nsproxy
 		return -EINVAL;
 
 	/* Threaded processes may not enter a different user namespace */
-	if (atomic_read(&current->mm->mm_users) > 1)
+	if (!current_is_single_threaded())
 		return -EINVAL;
 
 	if (current->fs->users != 1)
_

Patches currently in -mm which might be from rickyz@xxxxxxxxxxxx are

user_ns-use-correct-check-for-single-threadedness.patch

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