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selftests/nolibc: Check that snprintf() doesn't write beyond the buffer end

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Fill buf[] with known data and check the vsnprintf() doesn't write
beyond the specified buffer length.

Would have picked up the bug in field padding.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260302101815.3043-7-david.laight.linux@gmail.com
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
This commit is contained in:
David Laight
2026-03-02 10:17:58 +00:00
committed by Thomas Weißschuh
parent f36e1ec61a
commit 4ea2dedd50
1 changed files with 13 additions and 0 deletions
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13
tools/testing/selftests/nolibc/nolibc-test.c
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@@ -1679,6 +1679,10 @@ static int expect_vfprintf(int llen, const char *expected, const char *fmt, ...)
va_list args;
ssize_t w, expected_len;
/* Fill and terminate buf[] to check for overlong/absent writes */
memset(buf, 0xa5, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = 0;
va_start(args, fmt);
/* Limit buffer length to test truncation */
w = vsnprintf(buf, VFPRINTF_LEN + 1, fmt, args);
@@ -1710,6 +1714,15 @@ static int expect_vfprintf(int llen, const char *expected, const char *fmt, ...)
return 1;
}
/* Check for any overwrites after the actual data. */
while (++cmp_len < sizeof(buf) - 1) {
if ((unsigned char)buf[cmp_len] != 0xa5) {
llen += printf(" overwrote buf[%d] with 0x%x", cmp_len, buf[cmp_len]);
result(llen, FAIL);
return 1;
}
}
result(llen, OK);
return 0;
}