On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote:
+/*
+ * "memset(p, 0, size)" but for user space buffers. Caller must have already
+ * checked access_ok(p, size).
+ */
+static int __memzero_user(void __user *p, size_t s)
+{
+ const char zeros[BUFFER_SIZE] = {};
+ while (s > 0) {
+ size_t n = min(s, sizeof(zeros));
+
+ if (__copy_to_user(p, zeros, n))
+ return -EFAULT;
+
+ p += n;
+ s -= n;
+ }
+ return 0;
+}
That's called clear_user().
+int copy_struct_to_user(void __user *dst, size_t usize,
+ const void *src, size_t ksize)
+{
+ size_t size = min(ksize, usize);
+ size_t rest = abs(ksize - usize);
+
+ if (unlikely(usize > PAGE_SIZE))
+ return -EFAULT;
Why?
+ } else if (usize > ksize) {
+ if (__memzero_user(dst + size, rest))
+ return -EFAULT;
+ }
+ /* Copy the interoperable parts of the struct. */
+ if (__copy_to_user(dst, src, size))
+ return -EFAULT;
Why not simply clear_user() and copy_to_user()?
+int copy_struct_from_user(void *dst, size_t ksize,
+ const void __user *src, size_t usize)
+{
+ size_t size = min(ksize, usize);
+ size_t rest = abs(ksize - usize);
Cute, but... you would be just as well without that 'rest' thing.
+
+ if (unlikely(usize > PAGE_SIZE))
+ return -EFAULT;
Again, why?
+ if (unlikely(!access_ok(src, usize)))
+ return -EFAULT;
Why not simply copy_from_user() here?
+ /* Deal with trailing bytes. */
+ if (usize < ksize)
+ memset(dst + size, 0, rest);
+ else if (usize > ksize) {
+ const void __user *addr = src + size;
+ char buffer[BUFFER_SIZE] = {};
+
+ while (rest > 0) {
+ size_t bufsize = min(rest, sizeof(buffer));
+
+ if (__copy_from_user(buffer, addr, bufsize))
+ return -EFAULT;
+ if (memchr_inv(buffer, 0, bufsize))
+ return -E2BIG;
Frankly, that looks like a candidate for is_all_zeroes_user().
With the loop like above serving as a dumb default. And on
badly alighed address it _will_ be dumb. Probably too much
so - something like
if ((unsigned long)addr & 1) {
u8 v;
if (get_user(v, (__u8 __user *)addr))
return -EFAULT;
if (v)
return -E2BIG;
addr++;
}
if ((unsigned long)addr & 2) {
u16 v;
if (get_user(v, (__u16 __user *)addr))
return -EFAULT;
if (v)
return -E2BIG;
addr +=2;
}
if ((unsigned long)addr & 4) {
u32 v;
if (get_user(v, (__u32 __user *)addr))
return -EFAULT;
if (v)
return -E2BIG;
}
<read the rest like you currently do>
would be saner, and things like x86 could trivially add an
asm variant - it's not hard. Incidentally, memchr_inv() is
an overkill in this case...
