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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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Ricky Zhou <[email protected]>
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 <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Julien Tinnes <[email protected]>
Cc: <[email protected]> [3.9+]
Signed-off-by: Andrew Morton <[email protected]>
---
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(¤t->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(¤t->mm->mm_users) > 1)
+ if (!current_is_single_threaded())
return -EINVAL;
if (current->fs->users != 1)
_
Patches currently in -mm which might be from [email protected] are
user_ns-use-correct-check-for-single-threadedness.patch
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