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free row_buf/prev_row on frame re-entry in png_write_start_row #895

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free row_buf/prev_row on frame re-entry in png_write_start_row #895

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11 changes: 10 additions & 1 deletion pngwutil.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2045,7 +2045,14 @@ png_write_start_row(png_struct *png_ptr)
png_ptr->transformed_pixel_depth = png_ptr->pixel_depth;
png_ptr->maximum_pixel_depth = (png_byte)usr_pixel_depth;

/* Set up row buffer */
/* Set up row buffer. This function runs again for every APNG frame (see
* png_write_reset), so free any buffer left from a previous frame and clear
* the pointer before the allocation, matching png_read_start_row. Without
* this the previous frame's row_buf is leaked, and clearing first keeps a
* failed re-allocation from leaving a stale pointer that is freed twice.
*/
png_free(png_ptr, png_ptr->row_buf);
png_ptr->row_buf = NULL;
png_ptr->row_buf = png_voidcast(png_byte *, png_malloc(png_ptr, buf_size));

png_ptr->row_buf[0] = PNG_FILTER_VALUE_NONE;
Expand Down Expand Up @@ -2092,6 +2099,8 @@ png_write_start_row(png_struct *png_ptr)
/* We only need to keep the previous row if we are using one of the following
* filters.
*/
png_free(png_ptr, png_ptr->prev_row);
png_ptr->prev_row = NULL;
if ((filters & (PNG_FILTER_AVG | PNG_FILTER_UP | PNG_FILTER_PAETH)) != 0)
png_ptr->prev_row = png_voidcast(png_byte *,
png_calloc(png_ptr, buf_size));
Expand Down