On 19.11.2016 23:34, Michael Niedermayer wrote:
> On Sat, Nov 19, 2016 at 05:27:19PM +0100, Andreas Cadhalpun wrote:
>> diff --git a/libavcodec/smacker.c b/libavcodec/smacker.c
>> index b8a0c55..be3914b 100644
>> --- a/libavcodec/smacker.c
>> +++ b/libavcodec/smacker.c
>> @@ -129,8 +129,12 @@ static int smacker_decode_tree(GetBitContext *gb,
>> HuffContext *hc, uint32_t pref
>> /**
>> * Decode header tree
>> */
>> -static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc, DBCtx
>> *ctx)
>> +static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc, DBCtx
>> *ctx, int length)
>> {
>> + if(length > 5000) { // Larger length can cause segmentation faults due
>> to too deep recursion.
>> + av_log(NULL, AV_LOG_ERROR, "length too long\n");
>> + return AVERROR_INVALIDDATA;
>> + }
>
> are you sure this is not too large for some platforms ?
I don't think it's even possible to make this small enough for all cases,
as the stack size can be arbitrarily changed with 'ulimit -s'.
This value was chosen so that it works with the default stack size of 8 MB,
but if you think that's too much, it can be made smaller.
Attached is a variant reducing the 5000 to 500 and thus still working
with a stack size of only 0.8 MB.
Best regards,
Andreas
>From 031676592dc15ea11fd677d37d094772478a16e0 Mon Sep 17 00:00:00 2001
From: Andreas Cadhalpun <[email protected]>
Date: Sat, 19 Nov 2016 14:21:11 +0100
Subject: [PATCH] smacker: limit recursion depth of smacker_decode_bigtree
This fixes segmentation faults due to stack-overflow caused by too deep
recursion.
Signed-off-by: Andreas Cadhalpun <[email protected]>
---
libavcodec/smacker.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/libavcodec/smacker.c b/libavcodec/smacker.c
index b8a0c55..2d20be9 100644
--- a/libavcodec/smacker.c
+++ b/libavcodec/smacker.c
@@ -129,8 +129,12 @@ static int smacker_decode_tree(GetBitContext *gb, HuffContext *hc, uint32_t pref
/**
* Decode header tree
*/
-static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc, DBCtx *ctx)
+static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc, DBCtx *ctx, int length)
{
+ if(length > 500) { // Larger length can cause segmentation faults due to too deep recursion.
+ av_log(NULL, AV_LOG_ERROR, "length too long\n");
+ return AVERROR_INVALIDDATA;
+ }
if (hc->current + 1 >= hc->length) {
av_log(NULL, AV_LOG_ERROR, "Tree size exceeded!\n");
return AVERROR_INVALIDDATA;
@@ -159,12 +163,12 @@ static int smacker_decode_bigtree(GetBitContext *gb, HuffContext *hc, DBCtx *ctx
int r = 0, r_new, t;
t = hc->current++;
- r = smacker_decode_bigtree(gb, hc, ctx);
+ r = smacker_decode_bigtree(gb, hc, ctx, length + 1);
if(r < 0)
return r;
hc->values[t] = SMK_NODE | r;
r++;
- r_new = smacker_decode_bigtree(gb, hc, ctx);
+ r_new = smacker_decode_bigtree(gb, hc, ctx, length + 1);
if (r_new < 0)
return r_new;
return r + r_new;
@@ -275,7 +279,7 @@ static int smacker_decode_header_tree(SmackVContext *smk, GetBitContext *gb, int
goto error;
}
- if (smacker_decode_bigtree(gb, &huff, &ctx) < 0)
+ if (smacker_decode_bigtree(gb, &huff, &ctx, 0) < 0)
err = -1;
skip_bits1(gb);
if(ctx.last[0] == -1) ctx.last[0] = huff.current++;
--
2.10.2
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