Q: arch/mips && __secure_computing(sd) with sd != NULL
From: Oleg Nesterov
Date: Sat Jan 18 2025 - 11:23:22 EST
>From include/linux/seccomp.h
#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
extern int __secure_computing(const struct seccomp_data *sd);
in this case sd can be NULL, and only arch/mips/kernel/ptrace.c uses sd != NULL
#else
static inline int __secure_computing(const struct seccomp_data *sd)
{
secure_computing_strict(sd->nr);
return 0;
}
in this case __secure_computing(NULL) will crash. This looks confusing.
And unnecessary.
Now lets look at arch/mips/kernel/ptrace.c:syscall_trace_enter()
#ifdef CONFIG_SECCOMP
if (unlikely(test_thread_flag(TIF_SECCOMP))) {
int ret, i;
struct seccomp_data sd;
unsigned long args[6];
sd.nr = current_thread_info()->syscall;
sd.arch = syscall_get_arch(current);
syscall_get_arguments(current, regs, args);
for (i = 0; i < 6; i++)
sd.args[i] = args[i];
sd.instruction_pointer = KSTK_EIP(current);
ret = __secure_computing(&sd);
if (ret == -1)
return ret;
}
#endif
Why? arch/mips/Kconfig selects HAVE_ARCH_SECCOMP_FILTER so it can just do
#ifdef CONFIG_SECCOMP
if (unlikely(test_thread_flag(TIF_SECCOMP))) {
int ret = __secure_computing(NULL);
if (ret == -1)
return ret;
}
#endif
and rely on populate_seccomp_data() and sd == NULL checks in __secure_computing()
path ?
And given that arch/mips doesn't define CONFIG_GENERIC_ENTRY it can even do
int ret = secure_computing();
if (ret == -1)
return ret;
Did I miss something?
Note that if we change arch/mips we can do more cleanups, in particular
__secure_computing(sd) no longer needs the argument.
Oleg.