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>

2 files changed, 50 insertions, 52 deletions

diff --git a/arch/powerpc/kernel/sys_ppc32.c b/arch/powerpc/kernel/sys_ppc32.c
index b97c2d67f4ac..c5a4732bcc48 100644
--- a/arch/powerpc/kernel/sys_ppc32.c
+++ b/arch/powerpc/kernel/sys_ppc32.c
@@ -520,58 +520,6 @@ asmlinkage long compat_sys_umask(u32 mask)
         return sys_umask((int)mask);
 }
 
-#ifdef CONFIG_SYSCTL_SYSCALL
-struct __sysctl_args32 {
-        u32 name;
-        int nlen;
-        u32 oldval;
-        u32 oldlenp;
-        u32 newval;
-        u32 newlen;
-        u32 __unused[4];
-};
-
-asmlinkage long compat_sys_sysctl(struct __sysctl_args32 __user *args)
-{
-        struct __sysctl_args32 tmp;
-        int error;
-        size_t oldlen;
-        size_t __user *oldlenp = NULL;
-        unsigned long addr = (((unsigned long)&args->__unused[0]) + 7) & ~7;
-
-        if (copy_from_user(&tmp, args, sizeof(tmp)))
-                return -EFAULT;
-
-        if (tmp.oldval && tmp.oldlenp) {
-                /* Duh, this is ugly and might not work if sysctl_args
-                   is in read-only memory, but do_sysctl does indirectly
-                   a lot of uaccess in both directions and we'd have to
-                   basically copy the whole sysctl.c here, and
-                   glibc's __sysctl uses rw memory for the structure
-                   anyway.  */
-                oldlenp = (size_t __user *)addr;
-                if (get_user(oldlen, (compat_size_t __user *)compat_ptr(tmp.oldlenp)) ||
-                    put_user(oldlen, oldlenp))
-                        return -EFAULT;
-        }
-
-        lock_kernel();
-        error = do_sysctl(compat_ptr(tmp.name), tmp.nlen,
-                          compat_ptr(tmp.oldval), oldlenp,
-                          compat_ptr(tmp.newval), tmp.newlen);
-        unlock_kernel();
-        if (oldlenp) {
-                if (!error) {
-                        if (get_user(oldlen, oldlenp) ||
-                            put_user(oldlen, (compat_size_t __user *)compat_ptr(tmp.oldlenp)))
-                                error = -EFAULT;
-                }
-                copy_to_user(args->__unused, tmp.__unused, sizeof(tmp.__unused));
-        }
-        return error;
-}
-#endif
-
 unsigned long compat_sys_mmap2(unsigned long addr, size_t len,
                           unsigned long prot, unsigned long flags,
                           unsigned long fd, unsigned long pgoff)
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 */