[v10,2/4] seccomp: switch system call argument type to void *

Submitted by Tycho Andersen on Dec. 9, 2018, 6:24 p.m.

Details

Message ID 20181209182414.30862-3-tycho@tycho.ws
State New
Series "seccomp trap to userspace"
Headers show

Commit Message

Tycho Andersen Dec. 9, 2018, 6:24 p.m.
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 <tycho@tycho.ws>
CC: Kees Cook <keescook@chromium.org>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Eric W. Biederman <ebiederm@xmission.com>
CC: "Serge E. Hallyn" <serge@hallyn.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
CC: Christian Brauner <christian@brauner.io>
CC: Tyler Hicks <tyhicks@canonical.com>
CC: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
---
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(-)

Patch hide | download patch | download mbox

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:

Comments

Kees Cook Dec. 12, 2018, 12:31 a.m.
On Sun, Dec 9, 2018 at 10:24 AM Tycho Andersen <tycho@tycho.ws> 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 <tycho@tycho.ws>

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

> CC: Kees Cook <keescook@chromium.org>
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: Eric W. Biederman <ebiederm@xmission.com>
> CC: "Serge E. Hallyn" <serge@hallyn.com>
> Acked-by: Serge Hallyn <serge@hallyn.com>
> CC: Christian Brauner <christian@brauner.io>
> CC: Tyler Hicks <tyhicks@canonical.com>
> CC: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
> ---
> 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
>