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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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