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    Subject[PATCH v10 2/4] seccomp: switch system call argument type to void *
    Date
    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(-)

    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
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