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Subject[patch 22/87] futex: setup writeable mapping for futex ops which modify user space data
2.6.29-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Thomas Gleixner <tglx@linutronix.de>

commit 64d1304a64477629cb16b75491a77bafe6f86963 upstream.

The futex code installs a read only mapping via get_user_pages_fast()
even if the futex op function has to modify user space data. The
eventual fault was fixed up by futex_handle_fault() which walked the
VMA with mmap_sem held.

After the cleanup patches which removed the mmap_sem dependency of the
futex code commit 4dc5b7a36a49eff97050894cf1b3a9a02523717 (futex:
clean up fault logic) removed the private VMA walk logic from the
futex code. This change results in a stale RO mapping which is not
fixed up.

Instead of reintroducing the previous fault logic we set up the
mapping in get_user_pages_fast() read/write for all operations which
modify user space data. Also handle private futexes in the same way
and make the current unconditional access_ok(VERIFY_WRITE) depend on
the futex op.

Reported-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/futex.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -192,6 +192,7 @@ static void drop_futex_key_refs(union fu
* @shared: NULL for a PROCESS_PRIVATE futex,
* &current->mm->mmap_sem for a PROCESS_SHARED futex
* @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.
@@ -204,7 +205,8 @@ static void drop_futex_key_refs(union fu
* For other futexes, it points to &current->mm->mmap_sem and
* caller must have taken the reader lock. but NOT any spinlocks.
*/
-static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key)
+static int
+get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
@@ -227,7 +229,7 @@ static int get_futex_key(u32 __user *uad
* but access_ok() should be faster than find_vma()
*/
if (!fshared) {
- if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))))
+ if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
return -EFAULT;
key->private.mm = mm;
key->private.address = address;
@@ -236,7 +238,7 @@ static int get_futex_key(u32 __user *uad
}

again:
- err = get_user_pages_fast(address, 1, 0, &page);
+ err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page);
if (err < 0)
return err;

@@ -707,7 +709,7 @@ static int futex_wake(u32 __user *uaddr,
if (!bitset)
return -EINVAL;

- ret = get_futex_key(uaddr, fshared, &key);
+ ret = get_futex_key(uaddr, fshared, &key, VERIFY_READ);
if (unlikely(ret != 0))
goto out;

@@ -753,10 +755,10 @@ futex_wake_op(u32 __user *uaddr1, int fs
int ret, op_ret, attempt = 0;

retryfull:
- ret = get_futex_key(uaddr1, fshared, &key1);
+ ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
- ret = get_futex_key(uaddr2, fshared, &key2);
+ ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out_put_key1;

@@ -859,10 +861,10 @@ static int futex_requeue(u32 __user *uad
int ret, drop_count = 0;

retry:
- ret = get_futex_key(uaddr1, fshared, &key1);
+ ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
- ret = get_futex_key(uaddr2, fshared, &key2);
+ ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out_put_key1;

@@ -1181,7 +1183,7 @@ static int futex_wait(u32 __user *uaddr,
q.bitset = bitset;
retry:
q.key = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr, fshared, &q.key);
+ ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_READ);
if (unlikely(ret != 0))
goto out;

@@ -1370,7 +1372,7 @@ static int futex_lock_pi(u32 __user *uad
q.pi_state = NULL;
retry:
q.key = FUTEX_KEY_INIT;
- ret = get_futex_key(uaddr, fshared, &q.key);
+ ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out;

@@ -1630,7 +1632,7 @@ retry:
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
return -EPERM;

- ret = get_futex_key(uaddr, fshared, &key);
+ ret = get_futex_key(uaddr, fshared, &key, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out;




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