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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>
This commit is contained in:
Kees Cook 2016-06-01 19:29:15 -07:00
parent 8112c4f140
commit ce6526e8af
1 changed files with 18 additions and 3 deletions
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21
kernel/seccomp.c
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@ -556,7 +556,8 @@ void secure_computing_strict(int this_syscall)
#else
#ifdef CONFIG_SECCOMP_FILTER
static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
const bool recheck_after_trace)
{
u32 filter_ret, action;
int data;
@ -588,6 +589,10 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
goto skip;
case SECCOMP_RET_TRACE:
/* We've been put in this state by the ptracer already. */
if (recheck_after_trace)
return 0;
/* ENOSYS these calls if there is no tracer attached. */
if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
syscall_set_return_value(current,
@ -611,6 +616,15 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
if (this_syscall < 0)
goto skip;
/*
* Recheck the syscall, since it may have changed. This
* intentionally uses a NULL struct seccomp_data to force
* a reload of all registers. This does not goto skip since
* a skip would have already been reported.
*/
if (__seccomp_filter(this_syscall, NULL, true))
return -1;
return 0;
case SECCOMP_RET_ALLOW:
@ -629,7 +643,8 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
return -1;
}
#else
static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd)
static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
const bool recheck_after_trace)
{
BUG();
}
@ -652,7 +667,7 @@ int __secure_computing(const struct seccomp_data *sd)
__secure_computing_strict(this_syscall); /* may call do_exit */
return 0;
case SECCOMP_MODE_FILTER:
return __seccomp_filter(this_syscall, sd);
return __seccomp_filter(this_syscall, sd, false);
default:
BUG();
}