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ALSA: rawmidi: Fix potential Spectre v1 vulnerability

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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>
This commit is contained in:
Gustavo A. R. Silva 2019-03-20 16:15:24 -05:00 committed by Takashi Iwai
parent 667a8f7375
commit 2b1d9c8f87
1 changed files with 2 additions and 0 deletions
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sound/core/rawmidi.c
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@ -30,6 +30,7 @@
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/mm.h>
#include <linux/nospec.h>
#include <sound/rawmidi.h>
#include <sound/info.h>
#include <sound/control.h>
@ -601,6 +602,7 @@ static int __snd_rawmidi_info_select(struct snd_card *card,
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;