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    Subject[PATCH 4.4 104/131] ALSA: rawmidi: Fix potential Spectre v1 vulnerability
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Gustavo A. R. Silva <gustavo@embeddedor.com>

    commit 2b1d9c8f87235f593826b9cf46ec10247741fff9 upstream.

    info->stream is indirectly controlled by user-space, hence leading to
    a potential exploitation of the Spectre variant 1 vulnerability.

    This issue was detected with the help of Smatch:

    sound/core/rawmidi.c:604 __snd_rawmidi_info_select() warn: potential spectre issue 'rmidi->streams' [r] (local cap)

    Fix this by sanitizing info->stream before using it to index
    rmidi->streams.

    Notice that given that speculation windows are large, the policy is
    to kill the speculation on the first load and not worry if it can be
    completed with a dependent load/store [1].

    [1] https://lore.kernel.org/lkml/20180423164740.GY17484@dhcp22.suse.cz/

    Cc: stable@vger.kernel.org
    Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/core/rawmidi.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/sound/core/rawmidi.c
    +++ b/sound/core/rawmidi.c
    @@ -29,6 +29,7 @@
    #include <linux/mutex.h>
    #include <linux/module.h>
    #include <linux/delay.h>
    +#include <linux/nospec.h>
    #include <sound/rawmidi.h>
    #include <sound/info.h>
    #include <sound/control.h>
    @@ -591,6 +592,7 @@ static int __snd_rawmidi_info_select(str
    return -ENXIO;
    if (info->stream < 0 || info->stream > 1)
    return -EINVAL;
    + info->stream = array_index_nospec(info->stream, 2);
    pstr = &rmidi->streams[info->stream];
    if (pstr->substream_count == 0)
    return -ENOENT;

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