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vpx_img_flip() computes (d_h - 1) * stride to relocate the plane pointers. d_h is unsigned, so flipping an image with d_h == 0 underflows to UINT_MAX and produces a wild plane pointer ~64 GiB away from the buffer. d_h == 0 is reachable through the public API: vpx_img_wrap() accepted a zero height and vpx_img_set_rect() accepted a zero-area viewport, neither of which can ever be encoded (the encoders require the image size to match the configured size, which is always >= 1). Reject zero widths/heights in img_alloc_helper() (covers both vpx_img_alloc() and vpx_img_wrap()) and zero-area viewports in vpx_img_set_rect().
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vpx_img_flip() computes (d_h - 1) * stride to relocate the
plane pointers. d_h is unsigned, so flipping an image with
d_h == 0 underflows to UINT_MAX and produces a wild plane
pointer ~64 GiB away from the buffer.
d_h == 0 is reachable through the public API: vpx_img_wrap()
accepted a zero height and vpx_img_set_rect() accepted a
zero-area viewport, neither of which can ever be encoded
(the encoders require the image size to match the configured
size, which is always >= 1).
This patch rejects zero widths/heights in img_alloc_helper()
(covers both vpx_img_alloc() and vpx_img_wrap()) and
zero-area viewports in vpx_img_set_rect().
PoC (before the fix): wrapping a zero-height image and calling
vpx_img_flip() displaced the plane pointers by 68719476720
bytes (~64 GiB). After the fix the calls return NULL / fail
gracefully. Reproduced under ASan+UBSan; the change passes
the vpx_image_test suite (12/12).