From 04e5527eeca240ca81b0b95b58c50ef6a16b8030 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Mon, 27 May 2024 12:49:46 -0400
Subject: handle UB for invalid fflush() operations and mixing input and output
 without intervening fflush() or repositioning

---
 src/stdio/getc_unlocked.c | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'src/stdio/getc_unlocked.c')

diff --git a/src/stdio/getc_unlocked.c b/src/stdio/getc_unlocked.c
index 140e1a4d..0e68eb79 100644
--- a/src/stdio/getc_unlocked.c
+++ b/src/stdio/getc_unlocked.c
@@ -19,6 +19,12 @@ int getc_unlocked(FILE * stream)
 		return EOF;
 	}
 
+	if (stream->operation == OP_OUTPUT) {
+		UNDEFINED("attempted input on stream immediately after output");
+	}
+
+	stream->operation = OP_INPUT;
+
 	if (read(stream->fd, &c, sizeof(c)) != 1) {
 		stream->err = 1;
 		return EOF;
-- 
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