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    Subject[PATCH 4.17 201/220] ALSA: timer: Fix UBSAN warning at SNDRV_TIMER_IOCTL_NEXT_DEVICE ioctl
    Date
    4.17-stable review patch.  If anyone has any objections, please let me know.

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

    From: Takashi Iwai <tiwai@suse.de>

    commit b41f794f284966fd6ec634111e3b40d241389f96 upstream.

    The kernel may spew a WARNING about UBSAN undefined behavior at
    handling ALSA timer ioctl SNDRV_TIMER_IOCTL_NEXT_DEVICE:

    UBSAN: Undefined behaviour in sound/core/timer.c:1524:19
    signed integer overflow:
    2147483647 + 1 cannot be represented in type 'int'
    Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0x122/0x1c8 lib/dump_stack.c:113
    ubsan_epilogue+0x12/0x86 lib/ubsan.c:159
    handle_overflow+0x1c2/0x21f lib/ubsan.c:190
    __ubsan_handle_add_overflow+0x2a/0x31 lib/ubsan.c:198
    snd_timer_user_next_device sound/core/timer.c:1524 [inline]
    __snd_timer_user_ioctl+0x204d/0x2520 sound/core/timer.c:1939
    snd_timer_user_ioctl+0x67/0x95 sound/core/timer.c:1994
    ....

    It happens only when a value with INT_MAX is passed, as we're
    incrementing it unconditionally. So the fix is trivial, check the
    value with INT_MAX. Although the bug itself is fairly harmless, it's
    better to fix it so that fuzzers won't hit this again later.

    Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=200213
    Reported-and-tested-by: Team OWL337 <icytxw@gmail.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/core/timer.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/sound/core/timer.c
    +++ b/sound/core/timer.c
    @@ -1517,7 +1517,7 @@ static int snd_timer_user_next_device(st
    } else {
    if (id.subdevice < 0)
    id.subdevice = 0;
    - else
    + else if (id.subdevice < INT_MAX)
    id.subdevice++;
    }
    }

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