From af33d2433b03d63ed31fcfda842f46676a5e1afc Mon Sep 17 00:00:00 2001 From: Tycho Andersen Date: Sat, 8 Feb 2020 08:18:17 -0700 Subject: riscv: fix seccomp reject syscall code path If secure_computing() rejected a system call, we were previously setting the system call number to -1, to indicate to later code that the syscall failed. However, if something (e.g. a user notification) was sleeping, and received a signal, we may set a0 to -ERESTARTSYS and re-try the system call again. In this case, seccomp "denies" the syscall (because of the signal), and we would set a7 to -1, thus losing the value of the system call we want to restart. Instead, let's return -1 from do_syscall_trace_enter() to indicate that the syscall was rejected, so we don't clobber the value in case of -ERESTARTSYS or whatever. This commit fixes the user_notification_signal seccomp selftest on riscv to no longer hang. That test expects the system call to be re-issued after the signal, and it wasn't due to the above bug. Now that it is, everything works normally. Note that in the ptrace (tracer) case, the tracer can set the register values to whatever they want, so we still need to keep the code that handles out-of-bounds syscalls. However, we can drop the comment. We can also drop syscall_set_nr(), since it is no longer used anywhere, and the code that re-loads the value in a7 because of it. Reported in: https://lore.kernel.org/bpf/CAEn-LTp=ss0Dfv6J00=rCAy+N78U2AmhqJNjfqjr2FDpPYjxEQ@mail.gmail.com/ Reported-by: David Abdurachmanov Signed-off-by: Tycho Andersen Reviewed-by: Kees Cook Signed-off-by: Palmer Dabbelt --- arch/riscv/kernel/ptrace.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) (limited to 'arch/riscv/kernel/ptrace.c') diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c index 407464201b91..444dc7b0fd78 100644 --- a/arch/riscv/kernel/ptrace.c +++ b/arch/riscv/kernel/ptrace.c @@ -148,21 +148,19 @@ long arch_ptrace(struct task_struct *child, long request, * Allows PTRACE_SYSCALL to work. These are called from entry.S in * {handle,ret_from}_syscall. */ -__visible void do_syscall_trace_enter(struct pt_regs *regs) +__visible int do_syscall_trace_enter(struct pt_regs *regs) { if (test_thread_flag(TIF_SYSCALL_TRACE)) if (tracehook_report_syscall_entry(regs)) - syscall_set_nr(current, regs, -1); + return -1; /* * Do the secure computing after ptrace; failures should be fast. * If this fails we might have return value in a0 from seccomp * (via SECCOMP_RET_ERRNO/TRACE). */ - if (secure_computing() == -1) { - syscall_set_nr(current, regs, -1); - return; - } + if (secure_computing() == -1) + return -1; #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) @@ -170,6 +168,7 @@ __visible void do_syscall_trace_enter(struct pt_regs *regs) #endif audit_syscall_entry(regs->a7, regs->a0, regs->a1, regs->a2, regs->a3); + return 0; } __visible void do_syscall_trace_exit(struct pt_regs *regs) -- cgit v1.2.3