Commit message: Fix for CVE-2021-25291

* Invalid tile boundaries lead to OOB Read in TiffDecode.c, in TiffReadRGBATile
* Check the tile validity before attempting to read.
CVE: CVE-2021-25291
CWE: CWE-125
Vulnerability description: An issue was discovered in Pillow before 8.1.1. In TiffDecode.c, there is an out-of-bounds read in TiffreadRGBATile via invalid tile boundaries.

Project: Pillow
File: TiffDecode.c

ImagingLibTiffDecode(
    Imaging im, ImagingCodecState state, UINT8 *buffer, Py_ssize_t bytes) {
    TIFFSTATE *clientstate = (TIFFSTATE *)state->context;
    char *filename = "tempfile.tif";
    char *mode = "r";
    TIFF *tiff;
    uint16 photometric = 0;  // init to not PHOTOMETRIC_YCBCR
    int isYCbCr = 0;

    /* buffer is the encoded file, bytes is the length of the encoded file */
    /*     it all ends up in state->buffer, which is a uint8* from Imaging.h */

    TRACE(("in decoder: bytes %d\n", bytes));
    TRACE(
        ("State: count %d, state %d, x %d, y %d, ystep %d\n",
         state->count,
         state->state,
         state->x,
         state->y,
         state->ystep));
    TRACE(
        ("State: xsize %d, ysize %d, xoff %d, yoff %d \n",
         state->xsize,
         state->ysize,
         state->xoff,
         state->yoff));
    TRACE(("State: bits %d, bytes %d \n", state->bits, state->bytes));
    TRACE(
        ("Buffer: %p: %c%c%c%c\n",
         buffer,
         (char)buffer[0],
         (char)buffer[1],
         (char)buffer[2],
         (char)buffer[3]));
    TRACE(
        ("State->Buffer: %c%c%c%c\n",
         (char)state->buffer[0],
         (char)state->buffer[1],
         (char)state->buffer[2],
         (char)state->buffer[3]));
    TRACE(
        ("Image: mode %s, type %d, bands: %d, xsize %d, ysize %d \n",
         im->mode,
         im->type,
         im->bands,
         im->xsize,
         im->ysize));
    TRACE(
        ("Image: image8 %p, image32 %p, image %p, block %p \n",
         im->image8,
         im->image32,
         im->image,
         im->block));
    TRACE(("Image: pixelsize: %d, linesize %d \n", im->pixelsize, im->linesize));

    dump_state(clientstate);
    clientstate->size = bytes;
    clientstate->eof = clientstate->size;
    clientstate->loc = 0;
    clientstate->data = (tdata_t)buffer;
    clientstate->flrealloc = 0;
    dump_state(clientstate);

    TIFFSetWarningHandler(NULL);
    TIFFSetWarningHandlerExt(NULL);

    if (clientstate->fp) {
        TRACE(("Opening using fd: %d\n", clientstate->fp));
        lseek(clientstate->fp, 0, SEEK_SET);  // Sometimes, I get it set to the end.
        tiff = TIFFFdOpen(fd_to_tiff_fd(clientstate->fp), filename, mode);
    } else {
        TRACE(("Opening from string\n"));
        tiff = TIFFClientOpen(
            filename,
            mode,
            (thandle_t)clientstate,
            _tiffReadProc,
            _tiffWriteProc,
            _tiffSeekProc,
            _tiffCloseProc,
            _tiffSizeProc,
            _tiffMapProc,
            _tiffUnmapProc);
    }

    if (!tiff) {
        TRACE(("Error, didn't get the tiff\n"));
        state->errcode = IMAGING_CODEC_BROKEN;
        return -1;
    }

    if (clientstate->ifd) {
        int rv;
        uint32 ifdoffset = clientstate->ifd;
        TRACE(("reading tiff ifd %u\n", ifdoffset));
        rv = TIFFSetSubDirectory(tiff, ifdoffset);
        if (!rv) {
            TRACE(("error in TIFFSetSubDirectory"));
            goto decode_err;
        }
    }

    TIFFGetField(tiff, TIFFTAG_PHOTOMETRIC, &photometric);
    isYCbCr = photometric == PHOTOMETRIC_YCBCR;

    if (TIFFIsTiled(tiff)) {
        INT32 x, y, tile_y;
        UINT32 tile_width, tile_length, current_tile_length, current_line,
            current_tile_width, row_byte_size;
        UINT8 *new_data;

        TIFFGetField(tiff, TIFFTAG_TILEWIDTH, &tile_width);
        TIFFGetField(tiff, TIFFTAG_TILELENGTH, &tile_length);

        /* overflow check for row_byte_size calculation */
        if ((UINT32)INT_MAX / state->bits < tile_width) {
            state->errcode = IMAGING_CODEC_MEMORY;
            goto decode_err;
        }

        if (isYCbCr) {
            row_byte_size = tile_width * 4;
            /* sanity check, we use this value in shuffle below */
            if (im->pixelsize != 4) {
                state->errcode = IMAGING_CODEC_BROKEN;
                goto decode_err;
            }
        } else {
            // We could use TIFFTileSize, but for YCbCr data it returns subsampled data
            // size
            row_byte_size = (tile_width * state->bits + 7) / 8;
        }

        /* overflow check for realloc */
        if (INT_MAX / row_byte_size < tile_length) {
            state->errcode = IMAGING_CODEC_MEMORY;
            goto decode_err;
        }

        state->bytes = row_byte_size * tile_length;

        if (TIFFTileSize(tiff) > state->bytes) {
            // If the strip size as expected by LibTiff isn't what we're expecting,
            // abort.
            state->errcode = IMAGING_CODEC_MEMORY;
            goto decode_err;
        }

        /* realloc to fit whole tile */
        /* malloc check above */
        new_data = realloc(state->buffer, state->bytes);
        if (!new_data) {
            state->errcode = IMAGING_CODEC_MEMORY;
            goto decode_err;
        }

        state->buffer = new_data;

        TRACE(("TIFFTileSize: %d\n", state->bytes));

        for (y = state->yoff; y < state->ysize; y += tile_length) {
            for (x = state->xoff; x < state->xsize; x += tile_width) {
                if (isYCbCr) {
                    /* To avoid dealing with YCbCr subsampling, let libtiff handle it */
                    if (!TIFFReadRGBATile(tiff, x, y, (UINT32 *)state->buffer)) {
                        TRACE(("Decode Error, Tile at %dx%d\n", x, y));
                        state->errcode = IMAGING_CODEC_BROKEN;
                        goto decode_err;
                    }
                } else {
                    if (TIFFReadTile(tiff, (tdata_t)state->buffer, x, y, 0, 0) == -1) {
                        TRACE(("Decode Error, Tile at %dx%d\n", x, y));
                        state->errcode = IMAGING_CODEC_BROKEN;
                        goto decode_err;
                    }
                }

                TRACE(("Read tile at %dx%d; \n\n", x, y));

                current_tile_width = min((INT32)tile_width, state->xsize - x);
                current_tile_length = min((INT32)tile_length, state->ysize - y);
                // iterate over each line in the tile and stuff data into image
                for (tile_y = 0; tile_y < current_tile_length; tile_y++) {
                    TRACE(
                        ("Writing tile data at %dx%d using tile_width: %d; \n",
                         tile_y + y,
                         x,
                         current_tile_width));

                    // UINT8 * bbb = state->buffer + tile_y * row_byte_size;
                    // TRACE(("chars: %x%x%x%x\n", ((UINT8 *)bbb)[0], ((UINT8 *)bbb)[1],
                    // ((UINT8 *)bbb)[2], ((UINT8 *)bbb)[3]));
                    /*
                     * For some reason the TIFFReadRGBATile() function
                     * chooses the lower left corner as the origin.
                     * Vertically mirror by shuffling the scanlines
                     * backwards
                     */

                    if (isYCbCr) {
                        current_line = tile_length - tile_y - 1;
                    } else {
                        current_line = tile_y;
                    }

                    state->shuffle(
                        (UINT8 *)im->image[tile_y + y] + x * im->pixelsize,
                        state->buffer + current_line * row_byte_size,
                        current_tile_width);
                }
            }
        }
    } else {
        if (!isYCbCr) {
            _decodeStrip(im, state, tiff);
        } else {
            _decodeStripYCbCr(im, state, tiff);
        }
    }

decode_err:
    TIFFClose(tiff);
    TRACE(("Done Decoding, Returning \n"));
    // Returning -1 here to force ImageFile.load to break, rather than
    // even think about looping back around.
    return -1;
}