liblzma: Check for unexpected NULL pointers in block_header_decode().

The API docs gave an impression that such checks are done
but they actually weren't done. In practice it made little
difference since the calling code has a bug if these are NULL.

Thanks to Jia Tan for the original patch that checked for
block->filters == NULL.

diff --git a/src/liblzma/common/block_header_decoder.c b/src/liblzma/common/block_header_decoder.c
index 2e1135dd639a6f30fa7c83d2c26cdaeb765783f3..060479b468b07bdd970548768cee376e40eb132f 100644 (file)
--- a/src/liblzma/common/block_header_decoder.c
+++ b/src/liblzma/common/block_header_decoder.c
@@ -39,6 +39,10 @@ lzma_block_header_decode(lzma_block *block,
        // are invalid or over 63 bits, or if the header is too small
        // to contain the claimed information.
 
+       // Catch unexpected NULL pointers.
+       if (block == NULL || block->filters == NULL || in == NULL)
+               return LZMA_PROG_ERROR;
+
        // Initialize the filter options array. This way the caller can
        // safely free() the options even if an error occurs in this function.
        for (size_t i = 0; i <= LZMA_FILTERS_MAX; ++i) {