lib/lzma: Fix out-of-bounds read

Fix an out-of-bounds read in the LZMA decoder which happens when the src
buffer is too small to contain the 13-byte LZMA header.

Change-Id: Id5893e60fc9a48deb83560b7917f5558cd30ef4e
Signed-off-by: Alex Rebert <alexandre.rebert@gmail.com>
Found-by: Mayhem
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39085
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/lzma.c

@@ -29,6 +29,11 @@ size_t ulzman(const void *src, size_t srcn, void *dst, size_t dstn)
 	MAYBE_STATIC_BSS unsigned char scratchpad[15980];
 	const unsigned char *cp;
 
+	if (srcn < data_offset) {
+		printk(BIOS_WARNING, "lzma: Input too small.\n");
+		return 0;
+	}
+
 	memcpy(properties, src, LZMA_PROPERTIES_SIZE);
 	/* The outSize in LZMA stream is a 64bit integer stored in little-endian
 	 * (ref: lzma.cc@LZMACompress: put_64). To prevent accessing by