Re: [FFmpeg-devel] [PATCH] lavc/dovi_rpu: Fix UB for possible left shift of negative values

[Thilo Borgmann <thilo.borgmann@mail.de>]

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Am 16.06.22 um 11:44 schrieb Andreas Rheinhardt:
> Thilo Borgmann:
>> Hi,
>>
>> avoid left-shifting possibly negative values in case of RPU_COEFF_FLOAT.
>> Changed RPU_COEFF_FIXED as well for consistency.
>>
> 
> This is wrong: Both of your changes only affect RPU_COEFF_FIXED.

Indeed I'm sorry, got confused looking at the patch only when writing the commit msg.
It is actually changing get_ue_coef() for consistency although its all unsigned in there.

v2 attached.

Thanks,
Thilo

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From 55a3d1f1d276f3327c8920ec748fed79d8a98825 Mon Sep 17 00:00:00 2001
From: Michael Goulet <mgoulet@fb.com>
Date: Thu, 16 Jun 2022 12:02:02 +0200
Subject: [PATCH v2] lavc/dovi_rpu: Fix UB for possible left shift of negative
 values

It is undefined to left-shift a negative value.
Changed get_ue_coef() as well for consistency although its all positive values there.
---
 libavcodec/dovi_rpu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/dovi_rpu.c b/libavcodec/dovi_rpu.c
index a87562c8a3..833ce9e705 100644
--- a/libavcodec/dovi_rpu.c
+++ b/libavcodec/dovi_rpu.c
@@ -153,7 +153,7 @@ static inline uint64_t get_ue_coef(GetBitContext *gb, const AVDOVIRpuDataHeader
     case RPU_COEFF_FIXED:
         ipart = get_ue_golomb_long(gb);
         fpart.u32 = get_bits_long(gb, hdr->coef_log2_denom);
-        return (ipart << hdr->coef_log2_denom) + fpart.u32;
+        return ipart * (1 << hdr->coef_log2_denom) + fpart.u32;
 
     case RPU_COEFF_FLOAT:
         fpart.u32 = get_bits_long(gb, 32);
@@ -172,7 +172,7 @@ static inline int64_t get_se_coef(GetBitContext *gb, const AVDOVIRpuDataHeader *
     case RPU_COEFF_FIXED:
         ipart = get_se_golomb_long(gb);
         fpart.u32 = get_bits_long(gb, hdr->coef_log2_denom);
-        return (ipart << hdr->coef_log2_denom) + fpart.u32;
+        return ipart * (1 << hdr->coef_log2_denom) + fpart.u32;
 
     case RPU_COEFF_FLOAT:
         fpart.u32 = get_bits_long(gb, 32);
-- 
2.20.1 (Apple Git-117)


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