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Date: Wed, 20 Jan 2010 20:15:29 -0800
From: Greg KH <gregkh@...e.de>
To: linux-kernel@...r.kernel.org, stable@...nel.org
Cc: stable-review@...nel.org, torvalds@...ux-foundation.org,
akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Peter Zijlstra <peterz@...radead.org>,
Darren Hart <dvhltc@...ibm.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Nick Piggin <npiggin@...e.de>,
Ulrich Drepper <drepper@...il.com>, Ingo Molnar <mingo@...e.hu>
Subject: [08/30] futexes: Remove rw parameter from get_futex_key()
2.6.32-stable review patch. If anyone has any objections, please let us know.
------------------
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
commit 7485d0d3758e8e6491a5c9468114e74dc050785d upstream.
Currently, futexes have two problem:
A) The current futex code doesn't handle private file mappings properly.
get_futex_key() uses PageAnon() to distinguish file and
anon, which can cause the following bad scenario:
1) thread-A call futex(private-mapping, FUTEX_WAIT), it
sleeps on file mapping object.
2) thread-B writes a variable and it makes it cow.
3) thread-B calls futex(private-mapping, FUTEX_WAKE), it
wakes up blocked thread on the anonymous page. (but it's nothing)
B) Current futex code doesn't handle zero page properly.
Read mode get_user_pages() can return zero page, but current
futex code doesn't handle it at all. Then, zero page makes
infinite loop internally.
The solution is to use write mode get_user_page() always for
page lookup. It prevents the lookup of both file page of private
mappings and zero page.
Performance concerns:
Probaly very little, because glibc always initialize variables
for futex before to call futex(). It means glibc users never see
the overhead of this patch.
Compatibility concerns:
This patch has few compatibility issues. After this patch,
FUTEX_WAIT require writable access to futex variables (read-only
mappings makes EFAULT). But practically it's not a problem,
glibc always initalizes variables for futexes explicitly - nobody
uses read-only mappings.
Reported-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Acked-by: Darren Hart <dvhltc@...ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Nick Piggin <npiggin@...e.de>
Cc: Ulrich Drepper <drepper@...il.com>
LKML-Reference: <20100105162633.45A2.A69D9226@...fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
kernel/futex.c | 27 ++++++++++++---------------
1 file changed, 12 insertions(+), 15 deletions(-)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -203,8 +203,6 @@ static void drop_futex_key_refs(union fu
* @uaddr: virtual address of the futex
* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
* @key: address where result is stored.
- * @rw: mapping needs to be read/write (values: VERIFY_READ,
- * VERIFY_WRITE)
*
* Returns a negative error code or 0
* The key words are stored in *key on success.
@@ -216,7 +214,7 @@ static void drop_futex_key_refs(union fu
* lock_page() might sleep, the caller should not hold a spinlock.
*/
static int
-get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
+get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
@@ -239,7 +237,7 @@ get_futex_key(u32 __user *uaddr, int fsh
* but access_ok() should be faster than find_vma()
*/
if (!fshared) {
- if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
+ if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
return -EFAULT;
key->private.mm = mm;
key->private.address = address;
@@ -248,7 +246,7 @@ get_futex_key(u32 __user *uaddr, int fsh
}
again:
- err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page);
+ err = get_user_pages_fast(address, 1, 1, &page);
if (err < 0)
return err;
@@ -867,7 +865,7 @@ static int futex_wake(u32 __user *uaddr,
if (!bitset)
return -EINVAL;
- ret = get_futex_key(uaddr, fshared, &key, VERIFY_READ);
+ ret = get_futex_key(uaddr, fshared, &key);
if (unlikely(ret != 0))
goto out;
@@ -913,10 +911,10 @@ futex_wake_op(u32 __user *uaddr1, int fs
int ret, op_ret;
retry:
- ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
+ ret = get_futex_key(uaddr1, fshared, &key1);
if (unlikely(ret != 0))
goto out;
- ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
+ ret = get_futex_key(uaddr2, fshared, &key2);
if (unlikely(ret != 0))
goto out_put_key1;
@@ -1175,11 +1173,10 @@ retry:
pi_state = NULL;
}
- ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
+ ret = get_futex_key(uaddr1, fshared, &key1);
if (unlikely(ret != 0))
goto out;
- ret = get_futex_key(uaddr2, fshared, &key2,
- requeue_pi ? VERIFY_WRITE : VERIFY_READ);
+ ret = get_futex_key(uaddr2, fshared, &key2);
if (unlikely(ret != 0))
goto out_put_key1;
@@ -1738,7 +1735,7 @@ static int futex_wait_setup(u32 __user *
*/
retry:
q->key = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ);
+ ret = get_futex_key(uaddr, fshared, &q->key);
if (unlikely(ret != 0))
return ret;
@@ -1904,7 +1901,7 @@ static int futex_lock_pi(u32 __user *uad
q.requeue_pi_key = NULL;
retry:
q.key = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
+ ret = get_futex_key(uaddr, fshared, &q.key);
if (unlikely(ret != 0))
goto out;
@@ -2023,7 +2020,7 @@ retry:
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
return -EPERM;
- ret = get_futex_key(uaddr, fshared, &key, VERIFY_WRITE);
+ ret = get_futex_key(uaddr, fshared, &key);
if (unlikely(ret != 0))
goto out;
@@ -2215,7 +2212,7 @@ static int futex_wait_requeue_pi(u32 __u
rt_waiter.task = NULL;
key2 = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
+ ret = get_futex_key(uaddr2, fshared, &key2);
if (unlikely(ret != 0))
goto out;
--
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