On Fri, 14 Feb 2014 07:20:35 -0500
Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> It's possible for userland to pass down an iovec via writev() that has a
> bogus user pointer in it. If that happens and we're doing an uncached
> write, then we can end up getting less bytes than we expect from the
> call to iov_iter_copy_from_user.
>
> cifs_iovec_write isn't set up to handle that situation however. It'll
> blindly keep chugging through the page array and not filling those pages
> with anything useful. Worse yet, we'll later end up with a negative
> number in wdata->tailsz, which will confuse the sending routines and
> cause an oops at the very least.
>
> Fix this by having the copy phase of cifs_iovec_write stop copying data
> in this situation and send the last write as a short one. At the same
> time, we want to avoid sending a zero-length write to the server, so
> break out of the loop and set rc to -EFAULT if that happens. This also
> allows us to handle the case where no address in the iovec is valid.
>
> [Note: Marking this for stable on v3.4+ kernels, but kernels as old as
> v2.6.38 may have a similar problem and may need similar fix]
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.4+
> Reviewed-by: Pavel Shilovsky <piastry@xxxxxxxxxxx>
> Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/cifs/file.c | 37 ++++++++++++++++++++++++++++++++++---
> 1 file changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 03d1f454c713..ae1a4d58e672 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2387,7 +2387,7 @@ cifs_iovec_write(struct file *file, const struct iovec *iov,
> unsigned long nr_segs, loff_t *poffset)
> {
> unsigned long nr_pages, i;
> - size_t copied, len, cur_len;
> + size_t bytes, copied, len, cur_len;
> ssize_t total_written = 0;
> loff_t offset;
> struct iov_iter it;
> @@ -2442,14 +2442,45 @@ cifs_iovec_write(struct file *file, const struct iovec *iov,
>
> save_len = cur_len;
> for (i = 0; i < nr_pages; i++) {
> - copied = min_t(const size_t, cur_len, PAGE_SIZE);
> + bytes = min_t(const size_t, cur_len, PAGE_SIZE);
> copied = iov_iter_copy_from_user(wdata->pages[i], &it,
> - 0, copied);
> + 0, bytes);
> cur_len -= copied;
> iov_iter_advance(&it, copied);
> + /*
> + * If we didn't copy as much as we expected, then that
> + * may mean we trod into an unmapped area. Stop copying
> + * at that point. On the next pass through the big
> + * loop, we'll likely end up getting a zero-length
> + * write and bailing out of it.
> + */
> + if (copied < bytes)
> + break;
> }
> cur_len = save_len - cur_len;
>
> + /*
> + * If we have no data to send, then that probably means that
> + * the copy above failed altogether. That's most likely because
> + * the address in the iovec was bogus. Set the rc to -EFAULT,
> + * free anything we allocated and bail out.
> + */
> + if (!cur_len) {
> + for (i = 0; i < nr_pages; i++)
> + put_page(wdata->pages[i]);
> + kfree(wdata);
> + rc = -EFAULT;
> + break;
> + }
> +
> + /*
> + * i + 1 now represents the number of pages we actually used in
> + * the copy phase above. Bring nr_pages down to that, and free
> + * any pages that we didn't use.
> + */
> + for ( ; nr_pages > i + 1; nr_pages--)
> + put_page(wdata->pages[nr_pages - 1]);
> +
> wdata->sync_mode = WB_SYNC_ALL;
> wdata->nr_pages = nr_pages;
> wdata->offset = (__u64)offset;
By the way, I should note that this a fix for CVE-2014-0069. Steve,
mind adding that to the patch description?
Thanks,
--
Jeff Layton <jlayton@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
