[PATCH] futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

[PATCH] futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

[Andi Kleen]

futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

gup() requires mmap_sem, so take it before running it. The
recent fault_in_user_writeable() didn't do that.

I didn't find a good futex test case, so untested.

Likely a stable candidate.

Cc: npiggin@suse.de
Cc: tglx@linutronix.de
Cc: dvhltc@us.ibm.com
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
 kernel/futex.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux-2.6.32-ak/kernel/futex.c
===================================================================
--- linux-2.6.32-ak.orig/kernel/futex.c
+++ linux-2.6.32-ak/kernel/futex.c
@@ -304,8 +304,13 @@ void put_futex_key(int fshared, union fu
  */
 static int fault_in_user_writeable(u32 __user *uaddr)
 {
-	int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
+	int ret;
+	struct mm_struct *mm = current->mm;
+
+	down_read(&mm->mmap_sem);
+	ret = get_user_pages(current, mm, (unsigned long)uaddr,
 				 1, 1, 0, NULL, NULL);
+	up_read(&mm->mmap_sem);
 	return ret < 0 ? ret : 0;
 }
 

Re: [PATCH] futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

[Nick Piggin]

On Tue, Dec 08, 2009 at 01:19:42PM +0100, Andi Kleen wrote:
> futex: Take mmap_sem for get_user_pages in fault_in_user_writeable
> 
> gup() requires mmap_sem, so take it before running it. The
> recent fault_in_user_writeable() didn't do that.
> 
> I didn't find a good futex test case, so untested.
> 
> Likely a stable candidate.
> 
> Cc: npiggin@suse.de
> Cc: tglx@linutronix.de
> Cc: dvhltc@us.ibm.com
> Signed-off-by: Andi Kleen <ak@linux.intel.com>

I agree it should go to .stable.

Acked-by: Nick Piggin <npiggin@suse.de>


> ---
>  kernel/futex.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.32-ak/kernel/futex.c
> ===================================================================
> --- linux-2.6.32-ak.orig/kernel/futex.c
> +++ linux-2.6.32-ak/kernel/futex.c
> @@ -304,8 +304,13 @@ void put_futex_key(int fshared, union fu
>   */
>  static int fault_in_user_writeable(u32 __user *uaddr)
>  {
> -	int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
> +	int ret;
> +	struct mm_struct *mm = current->mm;
> +
> +	down_read(&mm->mmap_sem);
> +	ret = get_user_pages(current, mm, (unsigned long)uaddr,
>  				 1, 1, 0, NULL, NULL);
> +	up_read(&mm->mmap_sem);
>  	return ret < 0 ? ret : 0;
>  }
>  

[tip:core/urgent] futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

[tip-bot for Andi Kleen]

Commit-ID:  722d0172377a5697919b9f7e5beb95165b1dec4e
Gitweb:     http://git.kernel.org/tip/722d0172377a5697919b9f7e5beb95165b1dec4e
Author:     Andi Kleen <andi@firstfloor.org>
AuthorDate: Tue, 8 Dec 2009 13:19:42 +0100
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 8 Dec 2009 14:59:36 +0100

futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

get_user_pages() must be called with mmap_sem held.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: stable@kernel.org
Cc: Andrew Morton <akpm@linuxfoundation.org>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Darren Hart <dvhltc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20091208121942.GA21298@basil.fritz.box>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 kernel/futex.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index fb65e82..d73ef1f 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -304,8 +304,14 @@ void put_futex_key(int fshared, union futex_key *key)
  */
 static int fault_in_user_writeable(u32 __user *uaddr)
 {
-	int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
-				 1, 1, 0, NULL, NULL);
+	struct mm_struct *mm = current->mm;
+	int ret;
+
+	down_read(&mm->mmap_sem);
+	ret = get_user_pages(current, mm, (unsigned long)uaddr,
+			     1, 1, 0, NULL, NULL);
+	up_read(&mm->mmap_sem);
+
 	return ret < 0 ? ret : 0;
 }