[PATCH] futexs: fix infinite loop in get_futex_key on huge page

[PATCH] futexs: fix infinite loop in get_futex_key on huge page

[Sonny Rao]

get_futex_key() can infinitely loop if it is called on a virtual address
that is within a huge page but not aligned to the beginning of that
page.  The call to get_user_pages_fast will return the struct page for
a sub-page within the huge page and the check for page->mapping will
always fail.

The fix is to call compound_head on the page before checking that it's mapped.

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@kernel.org

Index: linux-2.6.31-rc2/kernel/futex.c
===================================================================
--- linux-2.6.31-rc2.orig/kernel/futex.c	2009-07-10 17:45:46.181084475 -0500
+++ linux-2.6.31-rc2/kernel/futex.c	2009-07-10 17:46:47.345084062 -0500
@@ -247,6 +247,7 @@
 	if (err < 0)
 		return err;
 
+	page = compound_head(page);
 	lock_page(page);
 	if (!page->mapping) {
 		unlock_page(page);

Re: [PATCH] futexs: fix infinite loop in get_futex_key on huge page

[Ingo Molnar]

* Sonny Rao <sonnyrao@us.ibm.com> wrote:

> get_futex_key() can infinitely loop if it is called on a virtual 
> address that is within a huge page but not aligned to the 
> beginning of that page.  The call to get_user_pages_fast will 
> return the struct page for a sub-page within the huge page and the 
> check for page->mapping will always fail.
> 
> The fix is to call compound_head on the page before checking that 
> it's mapped.
> 
> Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: stable@kernel.org
> 
> Index: linux-2.6.31-rc2/kernel/futex.c
> ===================================================================
> --- linux-2.6.31-rc2.orig/kernel/futex.c	2009-07-10 17:45:46.181084475 -0500
> +++ linux-2.6.31-rc2/kernel/futex.c	2009-07-10 17:46:47.345084062 -0500
> @@ -247,6 +247,7 @@
>  	if (err < 0)
>  		return err;
>  
> +	page = compound_head(page);
>  	lock_page(page);
>  	if (!page->mapping) {
>  		unlock_page(page);

Nice catch! Applied it to tip:core/urgent - Thomas, do you agree 
with the fix?

	Ingo

[tip:core/urgent] futexes: Fix infinite loop in get_futex_key() on huge page

[tip-bot for Sonny Rao]

Commit-ID:  7c8fa4f04ab956076605422d5ed37410893a8a73
Gitweb:     http://git.kernel.org/tip/7c8fa4f04ab956076605422d5ed37410893a8a73
Author:     Sonny Rao <sonnyrao@us.ibm.com>
AuthorDate: Fri, 10 Jul 2009 18:13:13 -0500
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 11 Jul 2009 10:18:45 +0200

futexes: Fix infinite loop in get_futex_key() on huge page

get_futex_key() can infinitely loop if it is called on a
virtual address that is within a huge page but not aligned to
the beginning of that page.  The call to get_user_pages_fast
will return the struct page for a sub-page within the huge page
and the check for page->mapping will always fail.

The fix is to call compound_head on the page before checking
that it's mapped.

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Cc: stable@kernel.org
Cc: anton@samba.org
Cc: rajamony@us.ibm.com
Cc: speight@us.ibm.com
Cc: mstephen@us.ibm.com
Cc: grimm@us.ibm.com
Cc: mikey@ozlabs.au.ibm.com
LKML-Reference: <20090710231313.GA23572@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 kernel/futex.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 794c862..0672ff8 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -247,6 +247,7 @@ again:
 	if (err < 0)
 		return err;
 
+	page = compound_head(page);
 	lock_page(page);
 	if (!page->mapping) {
 		unlock_page(page);

Re: [PATCH] futexs: fix infinite loop in get_futex_key on huge page

[Thomas Gleixner]

On Sat, 11 Jul 2009, Ingo Molnar wrote:
> 
> * Sonny Rao <sonnyrao@us.ibm.com> wrote:
> 
> > get_futex_key() can infinitely loop if it is called on a virtual 
> > address that is within a huge page but not aligned to the 
> > beginning of that page.  The call to get_user_pages_fast will 
> > return the struct page for a sub-page within the huge page and the 
> > check for page->mapping will always fail.
> > 
> > The fix is to call compound_head on the page before checking that 
> > it's mapped.
> > 
> > Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: stable@kernel.org
> > 
> > Index: linux-2.6.31-rc2/kernel/futex.c
> > ===================================================================
> > --- linux-2.6.31-rc2.orig/kernel/futex.c	2009-07-10 17:45:46.181084475 -0500
> > +++ linux-2.6.31-rc2/kernel/futex.c	2009-07-10 17:46:47.345084062 -0500
> > @@ -247,6 +247,7 @@
> >  	if (err < 0)
> >  		return err;
> >  
> > +	page = compound_head(page);
> >  	lock_page(page);
> >  	if (!page->mapping) {
> >  		unlock_page(page);
> 
> Nice catch! Applied it to tip:core/urgent - Thomas, do you agree 
> with the fix?

Acked-by-me.

[tip:core/urgent] futexes: Fix infinite loop in get_futex_key() on huge page

[tip-bot for Sonny Rao]

Commit-ID:  ce2ae53b750abfaa012ce408e93da131a5b5649b
Gitweb:     http://git.kernel.org/tip/ce2ae53b750abfaa012ce408e93da131a5b5649b
Author:     Sonny Rao <sonnyrao@us.ibm.com>
AuthorDate: Fri, 10 Jul 2009 18:13:13 -0500
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 11 Jul 2009 12:40:44 +0200

futexes: Fix infinite loop in get_futex_key() on huge page

get_futex_key() can infinitely loop if it is called on a
virtual address that is within a huge page but not aligned to
the beginning of that page.  The call to get_user_pages_fast
will return the struct page for a sub-page within the huge page
and the check for page->mapping will always fail.

The fix is to call compound_head on the page before checking
that it's mapped.

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
Cc: anton@samba.org
Cc: rajamony@us.ibm.com
Cc: speight@us.ibm.com
Cc: mstephen@us.ibm.com
Cc: grimm@us.ibm.com
Cc: mikey@ozlabs.au.ibm.com
LKML-Reference: <20090710231313.GA23572@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 kernel/futex.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 794c862..0672ff8 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -247,6 +247,7 @@ again:
 	if (err < 0)
 		return err;
 
+	page = compound_head(page);
 	lock_page(page);
 	if (!page->mapping) {
 		unlock_page(page);