sysctl: Introduce a generic compat sysctl sysctl

This uses compat_alloc_userspace to remove the various
hacks to allow do_sysctl to write to throuh oldlenp.

The rest of our mature compat syscall helper facitilies
are used as well to ensure we have a nice clean maintainable
compat syscall that can be used on all architectures.

The motiviation for a generic compat sysctl (besides the
obvious hack removal) is to reduce the number of compat
sysctl defintions out there so I can refactor the
binary sysctl implementation.

ppc already used the name compat_sys_sysctl so I remove the
ppcs version here.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 930a31cd708b..775cc49da622 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -176,3 +176,53 @@ SYSCALL_DEFINE1(sysctl, struct __sysctl_args __user *, args)
 
         return error;
 }
+
+#ifdef CONFIG_COMPAT
+#include <asm/compat.h>
+
+struct compat_sysctl_args {
+        compat_uptr_t   name;
+        int             nlen;
+        compat_uptr_t   oldval;
+        compat_uptr_t   oldlenp;
+        compat_uptr_t   newval;
+        compat_size_t   newlen;
+        compat_ulong_t  __unused[4];
+};
+
+asmlinkage long compat_sys_sysctl(struct compat_sysctl_args __user *args)
+{
+        struct compat_sysctl_args tmp;
+        compat_size_t __user *compat_oldlenp;
+        size_t __user *oldlenp = NULL;
+        size_t oldlen = 0;
+        ssize_t result;
+
+        if (copy_from_user(&tmp, args, sizeof(tmp)))
+                return -EFAULT;
+
+        compat_oldlenp = compat_ptr(tmp.oldlenp);
+        if (compat_oldlenp) {
+                oldlenp = compat_alloc_user_space(sizeof(*compat_oldlenp));
+
+                if (get_user(oldlen, compat_oldlenp) ||
+                    put_user(oldlen, oldlenp))
+                        return -EFAULT;
+        }
+
+        lock_kernel();
+        result = do_sysctl(compat_ptr(tmp.name), tmp.nlen,
+                           compat_ptr(tmp.oldval), oldlenp,
+                           compat_ptr(tmp.newval), tmp.newlen);
+        unlock_kernel();
+
+        if (oldlenp && !result) {
+                if (get_user(oldlen, oldlenp) ||
+                    put_user(oldlen, compat_oldlenp))
+                        return -EFAULT;
+        }
+
+        return result;
+}
+
+#endif /* CONFIG_COMPAT */