2023-07-26 06:37:45

by Thomas Weißschuh

Subject: [PATCH] selftests/nolibc: avoid buffer underrun in space printing

If the test description is longer than the status alignment the
parameter 'n' to putcharn() would lead to a signed underflow that then
gets converted to a very large unsigned value.
This in turn leads out-of-bound writes in memset() crashing the
application.

The failure case of EXPECT_PTRER() used in "mmap_bad" exhibits this
exact behavior.

Fixes: 8a27526f49f9 ("selftests/nolibc: add EXPECT_PTREQ, EXPECT_PTRNE and EXPECT_PTRER")
Signed-off-by: Thomas Weißschuh <[email protected]>
---
tools/testing/selftests/nolibc/nolibc-test.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 03b1d30f5507..9b76603e4ce3 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -151,7 +151,8 @@ static void result(int llen, enum RESULT r)
else
msg = "[FAIL]";

- putcharn(' ', 64 - llen);
+ if (llen < 64)
+ putcharn(' ', 64 - llen);
puts(msg);
}


---
base-commit: dfef4fc45d5713eb23d87f0863aff9c33bd4bfaf
change-id: 20230726-nolibc-result-width-1f4b0b4f3ca0

Best regards,
--
Thomas Weißschuh <[email protected]>

2023-07-29 09:11:10

by Willy Tarreau

Subject: Re: [PATCH] selftests/nolibc: avoid buffer underrun in space printing

On Wed, Jul 26, 2023 at 08:08:13AM +0200, Thomas Wei?schuh wrote:
> If the test description is longer than the status alignment the
> parameter 'n' to putcharn() would lead to a signed underflow that then
> gets converted to a very large unsigned value.
> This in turn leads out-of-bound writes in memset() crashing the
> application.
>
> The failure case of EXPECT_PTRER() used in "mmap_bad" exhibits this
> exact behavior.
>
> Fixes: 8a27526f49f9 ("selftests/nolibc: add EXPECT_PTREQ, EXPECT_PTRNE and EXPECT_PTRER")
> Signed-off-by: Thomas Wei?schuh <[email protected]>

Applied, thank you Thomas!
Willy