Re: [PATCH v10 2/4] seccomp: switch system call argument type to void *
From: Kees Cook <hidden>
Date: 2018-12-12 00:31:53
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On Sun, Dec 9, 2018 at 10:24 AM Tycho Andersen [off-list ref] wrote:
The const qualifier causes problems for any code that wants to write to the third argument of the seccomp syscall, as we will do in a future patch in this series. The third argument to the seccomp syscall is documented as void *, so rather than just dropping the const, let's switch everything to use void * as well. I believe this is safe because of 1. the documentation above, 2. there's no real type information exported about syscalls anywhere besides the man pages. Signed-off-by: Tycho Andersen <redacted>
Yeah, this can be void *, as you've found. I think it was just an artifact of the old filter code to use const char *. Applied for -next. -Kees
quoted hunk ↗ jump to hunk
CC: Kees Cook <redacted> CC: Andy Lutomirski <luto@amacapital.net> CC: Oleg Nesterov <oleg@redhat.com> CC: Eric W. Biederman <redacted> CC: "Serge E. Hallyn" <serge@hallyn.com> Acked-by: Serge Hallyn <serge@hallyn.com> CC: Christian Brauner <christian@brauner.io> CC: Tyler Hicks <redacted> CC: Akihiro Suda <redacted> --- v10: change type in include/linux/syscalls.h too to avoid compilation error in the !CONFIG_ARCH_HAS_SYSCALL_WRAPPER case --- include/linux/seccomp.h | 2 +- include/linux/syscalls.h | 2 +- kernel/seccomp.c | 8 ++++---- 3 files changed, 6 insertions(+), 6 deletions(-)diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h index e5320f6c8654..b5103c019cf4 100644 --- a/include/linux/seccomp.h +++ b/include/linux/seccomp.h@@ -43,7 +43,7 @@ extern void secure_computing_strict(int this_syscall); #endif extern long prctl_get_seccomp(void); -extern long prctl_set_seccomp(unsigned long, char __user *); +extern long prctl_set_seccomp(unsigned long, void __user *); static inline int seccomp_mode(struct seccomp *s) {diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 2ac3d13a915b..a60694fb0f58 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h@@ -879,7 +879,7 @@ asmlinkage long sys_renameat2(int olddfd, const char __user *oldname, int newdfd, const char __user *newname, unsigned int flags); asmlinkage long sys_seccomp(unsigned int op, unsigned int flags, - const char __user *uargs); + void __user *uargs); asmlinkage long sys_getrandom(char __user *buf, size_t count, unsigned int flags); asmlinkage long sys_memfd_create(const char __user *uname_ptr, unsigned int flags);diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 96afc32e041d..393e029f778a 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c@@ -924,7 +924,7 @@ static long seccomp_get_action_avail(const char __user *uaction) /* Common entry point for both prctl and syscall. */ static long do_seccomp(unsigned int op, unsigned int flags, - const char __user *uargs) + void __user *uargs) { switch (op) { case SECCOMP_SET_MODE_STRICT:@@ -944,7 +944,7 @@ static long do_seccomp(unsigned int op, unsigned int flags, } SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, - const char __user *, uargs) + void __user *, uargs) { return do_seccomp(op, flags, uargs); }@@ -956,10 +956,10 @@ SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, * * Returns 0 on success or -EINVAL on failure. */ -long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) +long prctl_set_seccomp(unsigned long seccomp_mode, void __user *filter) { unsigned int op; - char __user *uargs; + void __user *uargs; switch (seccomp_mode) { case SECCOMP_MODE_STRICT: --2.19.1
-- Kees Cook