um/ptrace: run seccomp after ptrace

Close the hole where ptrace can change a syscall out from under seccomp.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: user-mode-linux-devel@lists.sourceforge.net

diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index 9c5570f0f397d790b148ce7ab33a143e1720eea8..ef4b8f949b516df373b2d016e4a1366b53e1bc75 100644 (file)
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c
@@ -20,12 +20,12 @@ void handle_syscall(struct uml_pt_regs *r)
        UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
        PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
 
-       /* Do the secure computing check first; failures should be fast. */
-       if (secure_computing(NULL) == -1)
+       if (syscall_trace_enter(regs))
                return;
 
-       if (syscall_trace_enter(regs))
-               goto out;
+       /* Do the seccomp check after ptrace; failures should be fast. */
+       if (secure_computing(NULL) == -1)
+               return;
 
        /* Update the syscall number after orig_ax has potentially been updated
         * with ptrace.
@@ -37,6 +37,5 @@ void handle_syscall(struct uml_pt_regs *r)
                PT_REGS_SET_SYSCALL_RETURN(regs,
                                EXECUTE_SYSCALL(syscall, regs));
 
-out:
        syscall_trace_leave(regs);
 }