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ALSA: emux: Fix potential Spectre v1 vulnerabilities 

commit 4aea96f4237cea0c51a8bc87c0db31f0f932f1f0 upstream.

info.mode and info.port are indirectly controlled by user-space,
hence leading to a potential exploitation of the Spectre variant 1
vulnerability.

These issues were detected with the help of Smatch:

sound/synth/emux/emux_hwdep.c:72 snd_emux_hwdep_misc_mode() warn: potential spectre issue 'emu->portptrs[i]->ctrls' [w] (local cap)
sound/synth/emux/emux_hwdep.c:75 snd_emux_hwdep_misc_mode() warn: potential spectre issue 'emu->portptrs' [w] (local cap)
sound/synth/emux/emux_hwdep.c:75 snd_emux_hwdep_misc_mode() warn: potential spectre issue 'emu->portptrs[info.port]->ctrls' [w] (local cap)

Fix this by sanitizing both info.mode and info.port before using them
to index emu->portptrs[i]->ctrls, emu->portptrs[info.port]->ctrls and
emu->portptrs.

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://marc.info/?l=linux-kernel&m=152449131114778&w=2

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Gustavo A. R. Silva 2018-12-12 11:20:49 -06:00 committed by syphyr
parent 6dcc31529a
commit c0336ddcb0
1 changed files with 5 additions and 2 deletions
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7
sound/synth/emux/emux_hwdep.c
View File

@ -22,9 +22,9 @@
#include <sound/core.h>
#include <sound/hwdep.h>
#include <asm/uaccess.h>
#include <linux/nospec.h>
#include "emux_voice.h"
#define TMP_CLIENT_ID 0x1001
/*
@ -66,13 +66,16 @@ snd_emux_hwdep_misc_mode(struct snd_emux *emu, void __user *arg)
return -EFAULT;
if (info.mode < 0 || info.mode >= EMUX_MD_END)
return -EINVAL;
info.mode = array_index_nospec(info.mode, EMUX_MD_END);
if (info.port < 0) {
for (i = 0; i < emu->num_ports; i++)
emu->portptrs[i]->ctrls[info.mode] = info.value;
} else {
if (info.port < emu->num_ports)
if (info.port < emu->num_ports) {
info.port = array_index_nospec(info.port, emu->num_ports);
emu->portptrs[info.port]->ctrls[info.mode] = info.value;
}
}
return 0;
}