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Subject[PATCH 4.19 058/134] ALSA: seq: oss: Fix Spectre v1 vulnerability
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

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

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

commit c709f14f0616482b67f9fbcb965e1493a03ff30b upstream.

dev 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/seq/oss/seq_oss_synth.c:626 snd_seq_oss_synth_make_info() warn: potential spectre issue 'dp->synths' [w] (local cap)

Fix this by sanitizing dev before using it to index dp->synths.

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/seq/oss/seq_oss_synth.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/sound/core/seq/oss/seq_oss_synth.c
+++ b/sound/core/seq/oss/seq_oss_synth.c
@@ -617,13 +617,14 @@ int
snd_seq_oss_synth_make_info(struct seq_oss_devinfo *dp, int dev, struct synth_info *inf)
{
struct seq_oss_synth *rec;
+ struct seq_oss_synthinfo *info = get_synthinfo_nospec(dp, dev);

- if (dev < 0 || dev >= dp->max_synthdev)
+ if (!info)
return -ENXIO;

- if (dp->synths[dev].is_midi) {
+ if (info->is_midi) {
struct midi_info minf;
- snd_seq_oss_midi_make_info(dp, dp->synths[dev].midi_mapped, &minf);
+ snd_seq_oss_midi_make_info(dp, info->midi_mapped, &minf);
inf->synth_type = SYNTH_TYPE_MIDI;
inf->synth_subtype = 0;
inf->nr_voices = 16;

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