Re: [PATCH AUTOSEL 5.9 026/111] seccomp: kill process instead of thread for unknown actions

Kees Cook
2020-10-19T23:28:23Z

Hi Sasha,

I'd prefer this was not backported -- it's not a bug fix, and if the
behavioral change is actually disruptive, I'd like to keep the fall-out
contained. :)

Thanks!

-Kees

On Sun, Oct 18, 2020 at 03:16:42PM -0400, Sasha Levin wrote:
> From: Rich Felker <dalias@libc.org>
>
> [ Upstream commit 4d671d922d51907bc41f1f7f2dc737c928ae78fd ]
>
> Asynchronous termination of a thread outside of the userspace thread
> library's knowledge is an unsafe operation that leaves the process in
> an inconsistent, corrupt, and possibly unrecoverable state. In order
> to make new actions that may be added in the future safe on kernels
> not aware of them, change the default action from
> SECCOMP_RET_KILL_THREAD to SECCOMP_RET_KILL_PROCESS.
>
> Signed-off-by: Rich Felker <dalias@libc.org>
> Link: https://lore.kernel.org/r/20200829015609.GA32566@brightrain.aerifal.cx
> [kees: Fixed up coredump selection logic to match]
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> kernel/seccomp.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index 676d4af621038..f754c1087e413 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1020,7 +1020,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
> default:
> seccomp_log(this_syscall, SIGSYS, action, true);
> /* Dump core only if this is the last remaining thread. */
> - if (action == SECCOMP_RET_KILL_PROCESS ||
> + if (action != SECCOMP_RET_KILL_THREAD ||
> get_nr_threads(current) == 1) {
> kernel_siginfo_t info;
>
> @@ -1030,10 +1030,10 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
> seccomp_init_siginfo(&info, this_syscall, data);
> do_coredump(&info);
> }
> - if (action == SECCOMP_RET_KILL_PROCESS)
> - do_group_exit(SIGSYS);
> - else
> + if (action == SECCOMP_RET_KILL_THREAD)
> do_exit(SIGSYS);
> + else
> + do_group_exit(SIGSYS);
> }
>
> unreachable();
> --
> 2.25.1
>

--
Kees Cook