[PATCH] tools: kwboot: Fix quitting terminal

["Pali Rohár" <pali@kernel.org>]

Sometimes kwboot after quitting terminal prints error message:

  terminal: Bad address

This is caused by trying to call write() syscall with count of (size_t)-1
bytes.

When quit sequence is split into more read() calls then number of input
bytes (nin) at the end of cycle can underflow and be negative. Fix it.

Fixes: de7514046ea5 ("tools: kwboot: Fix detection of quit esc sequence")
Signed-off-by: Pali Rohár <pali@kernel.org>
---
 tools/kwboot.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/kwboot.c b/tools/kwboot.c
index 68c0ef1f1b07..2d2d545d8258 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -1197,7 +1197,7 @@ kwboot_term_pipe(int in, int out, const char *quit, int *s)
 			if (buf[i] == quit[*s]) {
 				(*s)++;
 				if (!quit[*s]) {
-					nin = i - *s;
+					nin = (i > *s) ? (i - *s) : 0;
 					break;
 				}
 			} else {
@@ -1208,7 +1208,7 @@ kwboot_term_pipe(int in, int out, const char *quit, int *s)
 		}
 
 		if (i == nin)
-			nin -= *s;
+			nin -= (nin > *s) ? *s : nin;
 	}
 
 	if (kwboot_write(out, buf, nin) < 0)
-- 
2.20.1