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    Subject[PATCH 5.9 042/391] futex: Fix incorrect should_fail_futex() handling
    Date
    From: Mateusz Nosek <mateusznosek0@gmail.com>

    [ Upstream commit 921c7ebd1337d1a46783d7e15a850e12aed2eaa0 ]

    If should_futex_fail() returns true in futex_wake_pi(), then the 'ret'
    variable is set to -EFAULT and then immediately overwritten. So the failure
    injection is non-functional.

    Fix it by actually leaving the function and returning -EFAULT.

    The Fixes tag is kinda blury because the initial commit which introduced
    failure injection was already sloppy, but the below mentioned commit broke
    it completely.

    [ tglx: Massaged changelog ]

    Fixes: 6b4f4bc9cb22 ("locking/futex: Allow low-level atomic operations to return -EAGAIN")
    Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Link: https://lore.kernel.org/r/20200927000858.24219-1-mateusznosek0@gmail.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/futex.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/kernel/futex.c b/kernel/futex.c
    index a5876694a60eb..39681bf8b06ca 100644
    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -1502,8 +1502,10 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_
    */
    newval = FUTEX_WAITERS | task_pid_vnr(new_owner);

    - if (unlikely(should_fail_futex(true)))
    + if (unlikely(should_fail_futex(true))) {
    ret = -EFAULT;
    + goto out_unlock;
    + }

    ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    if (!ret && (curval != uval)) {
    --
    2.27.0


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