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seccomp: recheck the syscall after RET_TRACE
When RET_TRACE triggers, a tracer may change a syscall into something that should be filtered by seccomp. This re-runs seccomp after a trace event to make sure things continue to pass. Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@kernel.org>
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@ -556,7 +556,8 @@ void secure_computing_strict(int this_syscall)
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#else
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#ifdef CONFIG_SECCOMP_FILTER
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static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
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static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
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const bool recheck_after_trace)
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{
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u32 filter_ret, action;
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int data;
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@ -588,6 +589,10 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
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goto skip;
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case SECCOMP_RET_TRACE:
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/* We've been put in this state by the ptracer already. */
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if (recheck_after_trace)
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return 0;
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/* ENOSYS these calls if there is no tracer attached. */
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if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
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syscall_set_return_value(current,
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@ -611,6 +616,15 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
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if (this_syscall < 0)
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goto skip;
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/*
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* Recheck the syscall, since it may have changed. This
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* intentionally uses a NULL struct seccomp_data to force
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* a reload of all registers. This does not goto skip since
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* a skip would have already been reported.
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*/
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if (__seccomp_filter(this_syscall, NULL, true))
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return -1;
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return 0;
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case SECCOMP_RET_ALLOW:
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@ -629,7 +643,8 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
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return -1;
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}
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#else
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static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
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static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
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const bool recheck_after_trace)
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{
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BUG();
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}
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@ -652,7 +667,7 @@ int __secure_computing(const struct seccomp_data *sd)
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__secure_computing_strict(this_syscall); /* may call do_exit */
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return 0;
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case SECCOMP_MODE_FILTER:
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return __seccomp_filter(this_syscall, sd);
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return __seccomp_filter(this_syscall, sd, false);
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default:
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BUG();
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}
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