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Commit 64d1304a authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

futex: setup writeable mapping for futex ops which modify user space data 



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: default avatarAndreas Schwab <schwab@linux-m68k.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
CC: stable@kernel.org
parent 279e677f

kernel/futex.c

+13 −11
Original line number Diff line number Diff line
@@ -193,6 +193,7 @@ static void drop_futex_key_refs(union futex_key *key) 
 * @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.
@@ -203,7 +204,8 @@ static void drop_futex_key_refs(union futex_key *key) 
 *

 * 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)

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;
@@ -226,7 +228,7 @@ static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key) 
	 *        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;
@@ -235,7 +237,7 @@ static int get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key) 
	}



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;
@@ -677,7 +679,7 @@ static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset) 
	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;
@@ -723,10 +725,10 @@ futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2, 
	int ret, op_ret;



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;
@@ -814,10 +816,10 @@ static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2, 
	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_READ);

	if (unlikely(ret != 0))

		goto out_put_key1;
@@ -1140,7 +1142,7 @@ static int futex_wait(u32 __user *uaddr, int fshared, 
	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;
@@ -1330,7 +1332,7 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared, 
	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;
@@ -1594,7 +1596,7 @@ static int futex_unlock_pi(u32 __user *uaddr, int fshared) 
	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;