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avcodec/asvenc: Fix crash with unaligned pointers/linesizes

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This happens on systems where get_pixels really needs
to be properly aligned, like ARMV7 or RISC-V. For these
systems, 0401ca714a caused
a bus error for the vsynth3-asv[12] tests, because
the stride in these tests is unaligned. See e.g.
https://fate.ffmpeg.org/report.cgi?slot=armv7-linux-gcc-13&time=20250527020548
https://fate.ffmpeg.org/report.cgi?slot=rv64gcvb-linux-gnu-gcc&time=20250527001827

It can also happen (even before said commit) if the pointers
itself are unaligned, e.g. by using the crop filter:
ffmpeg -filter_complex nullsrc=s=740x576:r=25,format=yuv420p,crop=w=720:x=2 \
-c:v asv2 -f null -

The alignment requirements for the frames passed to encoders are
mostly undocumented; the only thing I could find is the documentation
of AVFrame.linesize: "For video the linesizes should be multiples
of the CPUs alignment preference". This means that the FFmpeg cli
violates our API.

Yet as the above command line shows, it can also happen with
unaligned pointers and there does not seem to be a prohibition
of this, so we need to handle this case. This commit does so
by using get_pixels_unaligned when needed.

Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt
2025-05-27 15:38:17 +02:00
parent 9568e40aeb
commit 75960ac270
1 changed files with 17 additions and 6 deletions
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23
libavcodec/asvenc.c
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@ -45,6 +45,10 @@ typedef struct ASVEncContext {
PutBitContext pb;
void (*get_pixels)(int16_t *restrict block,
const uint8_t *pixels,
ptrdiff_t stride);
PixblockDSPContext pdsp;
FDCTDSPContext fdsp;
DECLARE_ALIGNED(32, int16_t, block)[6][64];
@ -219,16 +223,16 @@ static inline void dct_get(ASVEncContext *a, const AVFrame *frame,
const uint8_t *ptr_cb = frame->data[1] + (mb_y * 8 * frame->linesize[1]) + mb_x * 8;
const uint8_t *ptr_cr = frame->data[2] + (mb_y * 8 * frame->linesize[2]) + mb_x * 8;
a->pdsp.get_pixels(block[0], ptr_y, linesize);
a->pdsp.get_pixels(block[1], ptr_y + 8, linesize);
a->pdsp.get_pixels(block[2], ptr_y + 8 * linesize, linesize);
a->pdsp.get_pixels(block[3], ptr_y + 8 * linesize + 8, linesize);
a->get_pixels(block[0], ptr_y, linesize);
a->get_pixels(block[1], ptr_y + 8, linesize);
a->get_pixels(block[2], ptr_y + 8 * linesize, linesize);
a->get_pixels(block[3], ptr_y + 8 * linesize + 8, linesize);
for (i = 0; i < 4; i++)
a->fdsp.fdct(block[i]);
if (!(a->c.avctx->flags & AV_CODEC_FLAG_GRAY)) {
a->pdsp.get_pixels(block[4], ptr_cb, frame->linesize[1]);
a->pdsp.get_pixels(block[5], ptr_cr, frame->linesize[2]);
a->get_pixels(block[4], ptr_cb, frame->linesize[1]);
a->get_pixels(block[5], ptr_cr, frame->linesize[2]);
for (i = 4; i < 6; i++)
a->fdsp.fdct(block[i]);
}
@ -297,6 +301,13 @@ static int encode_frame(AVCodecContext *avctx, AVPacket *pkt,
if (ret < 0)
return ret;
if ((uintptr_t)pict->data[0] & 7 || pict->linesize[0] & 7 ||
(uintptr_t)pict->data[1] & 7 || pict->linesize[1] & 7 ||
(uintptr_t)pict->data[2] & 7 || pict->linesize[2] & 7)
a->get_pixels = a->pdsp.get_pixels_unaligned;
else
a->get_pixels = a->pdsp.get_pixels;
init_put_bits(&a->pb, pkt->data, pkt->size);
for (int mb_y = 0; mb_y < c->mb_height2; mb_y++) {