[lkml]   [2020]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC 2/4] lib/strncpy_from_user: Remove redundant user space pointer range check
On Tue, Jan 14, 2020 at 01:22:07PM -0800, Linus Torvalds wrote:

> The fact is, copying a string from user space is *very* different from
> copying a fixed number of bytes, and that whole dance with
> max_addr = user_addr_max();
> is absolutely required and necessary.
> You completely broke string copying.

BTW, a quick grep through the callers has found something odd -
static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
size_t size, loff_t *ppos)
char buf[64];
int buf_size;
int ret;

buf_size = min(size, (sizeof(buf) - 1));
if (strncpy_from_user(buf, user_buf, buf_size) < 0)
return -EFAULT;
buf[buf_size] = 0;

What the hell? If somebody is calling write(fd, buf, n) they'd
better be ready to see any byte from buf[0] up to buf[n - 1]
fetched, and if something is unmapped - deal with -EFAULT.
Is something really doing that and if so, why does kmemleak
try to accomodate that idiocy?

The same goes for several more ->write() instances - mtrr_write(),
armada_debugfs_crtc_reg_write() and cio_ignore_write(); IMO that's
seriously misguided (and cio one ought use vmemdup_user() instead
of what it's doing)...

 \ /
  Last update: 2020-01-15 00:47    [W:0.051 / U:1.776 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site