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From: | BALATON Zoltan |
Subject: | Re: [PATCH] ossaudio: fix out of bounds write |
Date: | Thu, 9 Jul 2020 03:08:31 +0200 (CEST) |
User-agent: | Alpine 2.22 (BSF 395 2020-01-19) |
On Wed, 8 Jul 2020, Philippe Mathieu-Daudé wrote:
On 7/7/20 8:08 PM, Volker Rümelin wrote:In function oss_read() a read error currently does not exit the read loop. With no data to read the variable pos will quickly underflow and a subsequent successful read overwrites memory outside the buffer. This patch adds the missing break statement to the error path of the function.Correct, but ...To reproduce start qemu with -audiodev oss,id=audio0 and in the guest start audio recording. After some time this will trigger an exception. Fixes: 3ba4066d08 "ossaudio: port to the new audio backend api" Signed-off-by: Volker Rümelin <vr_qemu@t-online.de> --- audio/ossaudio.c | 1 + 1 file changed, 1 insertion(+) diff --git a/audio/ossaudio.c b/audio/ossaudio.c index f88d076ec2..a7dcaa31ad 100644 --- a/audio/ossaudio.c +++ b/audio/ossaudio.c @@ -691,6 +691,7 @@ static size_t oss_read(HWVoiceIn *hw, void *buf, size_t len) len, dst); break; } + break;
Maybe it would be less confusing if you converted the switch(errno) to an if then you wouldn't have two senses of break; in close proximity. I was thinking something like
if (nread == -1) { if (errno != EINTR && errno != EAGAIN) { logerr(); } break; /* from while, which is now clear */ }
} pos += nread;... now pos += -1, then the size returned misses the last byte.
Don't you break from loop in if () above this so -1 is never added to pos after this patch? What happens for EINTR and EAGAIN? Now we break from the loop for those too, should it be continue; instead?
Regards, BALATON Zoltan
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