diff --git a/stb_image.h b/stb_image.h index 9a032c7..da378cb 100644 --- a/stb_image.h +++ b/stb_image.h @@ -5535,9 +5535,23 @@ static void *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int req psize = (info.offset - info.extra_read - info.hsz) >> 2; } if (psize == 0) { - if (info.offset != s->callback_already_read + (s->img_buffer - s->img_buffer_original)) { - return stbi__errpuc("bad offset", "Corrupt BMP"); - } + // accept some number of extra bytes after the header, but if the offset points either to before + // the header ends or implies a large amount of extra data, reject the file as malformed + int bytes_read_so_far = s->callback_already_read + (int)(s->img_buffer - s->img_buffer_original); + int header_limit = 1024; // max we actually read is below 256 bytes currently. + int extra_data_limit = 256*4; // what ordinarily goes here is a palette; 256 entries*4 bytes is its max size. + if (bytes_read_so_far <= 0 || bytes_read_so_far > header_limit) { + return stbi__errpuc("bad header", "Corrupt BMP"); + } + // we established that bytes_read_so_far is positive and sensible. + // the first half of this test rejects offsets that are either too small positives, or + // negative, and guarantees that info.offset >= bytes_read_so_far > 0. this in turn + // ensures the number computed in the second half of the test can't overflow. + if (info.offset < bytes_read_so_far || info.offset - bytes_read_so_far > extra_data_limit) { + return stbi__errpuc("bad offset", "Corrupt BMP"); + } else { + stbi__skip(s, info.offset - bytes_read_so_far); + } } if (info.bpp == 24 && ma == 0xff000000)