main: prevent invalid memory access when executing empty stdin

In case the ucode cli executes stdin with zero bytes length, ensure to
pass a dummy string instead of a NULL pointer to uc_source_new_buffer()
to prevent libc's fmemopen() from writing to nonexistent memory.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 8 insertions, 0 deletions

diff --git a/main.c b/main.c
index a51c370..96f4adb 100644
--- a/main.c
+++ b/main.c
@@ -201,6 +201,14 @@ read_stdin(void)
 
 	stdin_unused = NULL;
 
+	/* On empty stdin, provide a dummy buffer and ensure that it is
+	 * at least one byte long, due to
+	 * https://github.com/google/sanitizers/issues/627 */
+	if (p == NULL) {
+		p = xstrdup("\n");
+		tlen = 1;
+	}
+
 	return uc_source_new_buffer("[stdin]", p, tlen);
 }