On Thu, May 13, 2021 at 6:23 PM Thadeu Lima de Souza Cascardo
<cascardo@xxxxxxxxxxxxx> wrote:
>
> One the mmap tests will map a single page, then try to extend the
> mapping by use of mremap, which should fail. Right after that, it unmaps
> the extended area, which may end up unmapping other valid mapped areas,
> this causing a segfault.
>
> Only unmap the area that is expected to be mapped.
>
> Fixes: b2fb299c9aa4 ("selftests/bpf: test ringbuf mmap read-only and read-write restrictions")
We backed out this patch because it was causing our CI to crash on the
ringbuf test. I think you found out why :)
I'm going to incorporate your fix into my patch and leave your and
mine Signed-off-by and post it upstream. Hope that works fine for
attribution? And thanks for catching this!
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
> ---
> tools/testing/selftests/bpf/prog_tests/ringbuf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> index 197e30b83298..f9a8ae331963 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> @@ -146,7 +146,7 @@ void test_ringbuf(void)
> ASSERT_ERR(mprotect(mmap_ptr, page_size, PROT_WRITE), "write_protect");
> ASSERT_ERR(mprotect(mmap_ptr, page_size, PROT_EXEC), "exec_protect");
> ASSERT_ERR_PTR(mremap(mmap_ptr, 0, 3 * page_size, MREMAP_MAYMOVE), "ro_remap");
> - ASSERT_OK(munmap(mmap_ptr, 3 * page_size), "unmap_ro");
> + ASSERT_OK(munmap(mmap_ptr, page_size), "unmap_ro");
>
> /* only trigger BPF program for current process */
> skel->bss->pid = getpid();
> --
> 2.30.2
>
