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

From: Tycho Andersen
Date: Sun Dec 09 2018 - 13:24:34 EST

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

Signed-off-by: Tycho Andersen <tycho@xxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
CC: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
CC: Christian Brauner <christian@xxxxxxxxxx>
CC: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
CC: Akihiro Suda <suda.akihiro@xxxxxxxxxxxxx>
v10: change type in include/linux/syscalls.h too to avoid compilation error
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);

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) {
@@ -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) {