tools: kwboot: Fix buffer overflow in kwboot_terminal()

The `in` variable is set to -1 in kwboot_terminal() if stdin is not a
tty. In this case we should not look whether -1 is set in fd_set, for it
can lead to a buffer overflow, which can be reproduced with
  echo "xyz" | ./tools/kwboot -t /dev/ttyUSB0

Signed-off-by: Marek Behún <[email protected]>
Reviewed-by: Stefan Roese <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/tools/kwboot.c b/tools/kwboot.c
index 7feeaa45a22..e6e99849a79 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -552,7 +552,7 @@ kwboot_terminal(int tty)
 				break;
 		}
 
-		if (FD_ISSET(in, &rfds)) {
+		if (in >= 0 && FD_ISSET(in, &rfds)) {
 			rc = kwboot_term_pipe(in, tty, quit, &s);
 			if (rc)
 				break;