Commit a53ba068 authored Dec 12, 2018 by Gustavo A. R. Silva Committed by Greg Kroah-Hartman Jan 09, 2019

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>
Cc: stable@vger.kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent bbf03612

sound/synth/emux/emux_hwdep.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -22,9 +22,9 @@
		#include <sound/core.h>
		#include <sound/hwdep.h>
		#include <linux/uaccess.h>
		#include <linux/nospec.h>
		#include "emux_voice.h"


		#define TMP_CLIENT_ID 0x1001

		/*
		@@ -66,14 +66,17 @@ 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;
		}