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saner copy_mount_options()

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don't bother with the byte-by-byte loops, etc.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2020-01-20 19:49:57 -05:00
parent 324282c025
commit 12efec5602
1 changed files with 7 additions and 42 deletions
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49
fs/namespace.c
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@ -2979,39 +2979,10 @@ static void shrink_submounts(struct mount *mnt)
}
}
/*
* Some copy_from_user() implementations do not return the exact number of
* bytes remaining to copy on a fault. But copy_mount_options() requires that.
* Note that this function differs from copy_from_user() in that it will oops
* on bad values of `to', rather than returning a short copy.
*/
static long exact_copy_from_user(void *to, const void __user * from,
unsigned long n)
{
char *t = to;
const char __user *f = from;
char c;
if (!access_ok(from, n))
return n;
while (n) {
if (__get_user(c, f)) {
memset(t, 0, n);
break;
}
*t++ = c;
f++;
n--;
}
return n;
}
void *copy_mount_options(const void __user * data)
{
int i;
unsigned long size;
char *copy;
unsigned size;
if (!data)
return NULL;
@ -3020,22 +2991,16 @@ void *copy_mount_options(const void __user * data)
if (!copy)
return ERR_PTR(-ENOMEM);
/* We only care that *some* data at the address the user
* gave us is valid. Just in case, we'll zero
* the remainder of the page.
*/
/* copy_from_user cannot cross TASK_SIZE ! */
size = TASK_SIZE - (unsigned long)untagged_addr(data);
if (size > PAGE_SIZE)
size = PAGE_SIZE;
size = PAGE_SIZE - offset_in_page(data);
i = size - exact_copy_from_user(copy, data, size);
if (!i) {
if (copy_from_user(copy, data, size)) {
kfree(copy);
return ERR_PTR(-EFAULT);
}
if (i != PAGE_SIZE)
memset(copy + i, 0, PAGE_SIZE - i);
if (size != PAGE_SIZE) {
if (copy_from_user(copy + size, data + size, PAGE_SIZE - size))
memset(copy + size, 0, PAGE_SIZE - size);
}
return copy;
}