2022-03-21 22:05:40

by Jann Horn

Subject: [PATCH] selftests/seccomp: Don't call read() on TTY from background pgrp

Since commit 92d25637a3a4 ("kselftest: signal all child processes"), tests
are executed in background process groups. This means that trying to read
from stdin now throws SIGTTIN when stdin is a TTY, which breaks some
seccomp selftests that try to use read(0, NULL, 0) as a dummy syscall.

The simplest way to fix that is probably to just use -1 instead of 0 as
the dummy read()'s FD.

Fixes: 92d25637a3a4 ("kselftest: signal all child processes")
Signed-off-by: Jann Horn <[email protected]>
---
tools/testing/selftests/seccomp/seccomp_bpf.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 9d126d7fabdb..313bb0cbfb1e 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -955,7 +955,7 @@ TEST(ERRNO_valid)
ASSERT_EQ(0, ret);

EXPECT_EQ(parent, syscall(__NR_getppid));
- EXPECT_EQ(-1, read(0, NULL, 0));
+ EXPECT_EQ(-1, read(-1, NULL, 0));
EXPECT_EQ(E2BIG, errno);
}

@@ -974,7 +974,7 @@ TEST(ERRNO_zero)

EXPECT_EQ(parent, syscall(__NR_getppid));
/* "errno" of 0 is ok. */
- EXPECT_EQ(0, read(0, NULL, 0));
+ EXPECT_EQ(0, read(-1, NULL, 0));
}

/*
@@ -995,7 +995,7 @@ TEST(ERRNO_capped)
ASSERT_EQ(0, ret);

EXPECT_EQ(parent, syscall(__NR_getppid));
- EXPECT_EQ(-1, read(0, NULL, 0));
+ EXPECT_EQ(-1, read(-1, NULL, 0));
EXPECT_EQ(4095, errno);
}

@@ -1026,7 +1026,7 @@ TEST(ERRNO_order)
ASSERT_EQ(0, ret);

EXPECT_EQ(parent, syscall(__NR_getppid));
- EXPECT_EQ(-1, read(0, NULL, 0));
+ EXPECT_EQ(-1, read(-1, NULL, 0));
EXPECT_EQ(12, errno);
}

@@ -2623,7 +2623,7 @@ void *tsync_sibling(void *data)
ret = prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0);
if (!ret)
return (void *)SIBLING_EXIT_NEWPRIVS;
- read(0, NULL, 0);
+ read(-1, NULL, 0);
return (void *)SIBLING_EXIT_UNKILLED;
}


base-commit: 34e047aa16c0123bbae8e2f6df33e5ecc1f56601
--
2.35.1.894.gb6a874cedc-goog

2022-03-25 15:28:32

by Kees Cook

Subject: Re: [PATCH] selftests/seccomp: Don't call read() on TTY from background pgrp

On Sat, 19 Mar 2022 02:00:11 +0100, Jann Horn wrote:
> Since commit 92d25637a3a4 ("kselftest: signal all child processes"), tests
> are executed in background process groups. This means that trying to read
> from stdin now throws SIGTTIN when stdin is a TTY, which breaks some
> seccomp selftests that try to use read(0, NULL, 0) as a dummy syscall.
>
> The simplest way to fix that is probably to just use -1 instead of 0 as
> the dummy read()'s FD.
>
> [...]

Applied to for-next/seccomp, thanks!

[1/1] selftests/seccomp: Don't call read() on TTY from background pgrp
https://git.kernel.org/kees/c/1d27adee48cf

--
Kees Cook