Regression since: 3ba570de8b (port from MMX to SSE2).
The SSE2 inline asm in libavfilter/x86/vf_noise.c (line_noise_sse2 and
line_noise_avg_sse2) uses aligned loads/stores (movdqa, movntdq) but never
checks pointer alignment. When the filter reuses an input frame (common
path when av_frame_is_writable() is true), it may receive misaligned data
from upstream filters that adjust frame->data[i] in place, notably vf_crop:
- vf_crop adjusts plane pointers by arbitrary byte offsets
(frame->data[plane] += ...), so an x offset of 1 on 8-bit formats produces
a 1‑byte misalignment.
- The noise filter then calls the SSE2 path directly on those pointers
without realigning or falling back.
Repro on x86_64/SSE2 (current HEAD at that commit):
./ffmpeg -v error -f lavfi -i testsrc=s=320x240:rate=1 \
-vf "format=yuv420p,crop=w=319:x=1:h=240:exact=1,noise=alls=50" \
-frames:v 1 -f null -
This crashes with SIGSEGV at the aligned load in line_noise_sse2 (movdqa
(%r9,%rax),%xmm0; effective address misaligned by 1 byte).
Impact: denial of service via crafted filtergraphs (e.g., crop + noise).
Applies to planar 8-bit formats where upstream filters can shift data
pointers without reallocating.
Found-by: Pwno OSS Team
cc43670268