From: Eric W. Biederman ebiederm@xmission.com
commit 941edc5bf174b67f94db19817cbeab0a93e0c32a upstream.
Use force_fatal_sig instead of calling do_exit directly. This ensures the ordinary signal handling path gets invoked, core dumps as appropriate get created, and for multi-threaded processes all of the threads are terminated not just a single thread.
When asked Gabriel Krisman Bertazi krisman@collabora.com said [1]:
ebiederm@xmission.com (Eric W. Biederman) asked:
Why does do_syscal_user_dispatch call do_exit(SIGSEGV) and do_exit(SIGSYS) instead of force_sig(SIGSEGV) and force_sig(SIGSYS)?
Looking at the code these cases are not expected to happen, so I would be surprised if userspace depends on any particular behaviour on the failure path so I think we can change this.
Hi Eric,
There is not really a good reason, and the use case that originated the feature doesn't rely on it.
Unless I'm missing yet another problem and others correct me, I think it makes sense to change it as you described.
Is using do_exit in this way something you copied from seccomp?
I'm not sure, its been a while, but I think it might be just that. The first prototype of SUD was implemented as a seccomp mode.
If at some point it becomes interesting we could relax "force_fatal_sig(SIGSEGV)" to instead say "force_sig_fault(SIGSEGV, SEGV_MAPERR, sd->selector)".
I avoid doing that in this patch to avoid making it possible to catch currently uncatchable signals.
Cc: Gabriel Krisman Bertazi krisman@collabora.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Peter Zijlstra peterz@infradead.org Cc: Andy Lutomirski luto@kernel.org [1] https://lkml.kernel.org/r/87mtr6gdvi.fsf@collabora.com Link: https://lkml.kernel.org/r/20211020174406.17889-14-ebiederm@xmission.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Cc: Thomas Backlund tmb@iki.fi Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/entry/syscall_user_dispatch.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/kernel/entry/syscall_user_dispatch.c +++ b/kernel/entry/syscall_user_dispatch.c @@ -47,14 +47,18 @@ bool syscall_user_dispatch(struct pt_reg * access_ok() is performed once, at prctl time, when * the selector is loaded by userspace. */ - if (unlikely(__get_user(state, sd->selector))) - do_exit(SIGSEGV); + if (unlikely(__get_user(state, sd->selector))) { + force_fatal_sig(SIGSEGV); + return true; + }
if (likely(state == SYSCALL_DISPATCH_FILTER_ALLOW)) return false;
- if (state != SYSCALL_DISPATCH_FILTER_BLOCK) - do_exit(SIGSYS); + if (state != SYSCALL_DISPATCH_FILTER_BLOCK) { + force_fatal_sig(SIGSYS); + return true; + } }
sd->on_dispatch = true;