lkml.org 
[lkml]   [2023]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH net] udp: Fix __ip_append_data()'s handling of MSG_SPLICE_PAGES
Date
Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:

> copy -= -fraggap definitely seems off. You point out that it even can
> turn length negative?

Yes. See the logging I posted:

==>splice_to_socket() 6630
udp_sendmsg(8,8)
__ip_append_data(copy=-1,len=8, mtu=8192 skblen=8189 maxfl=8188)
pagedlen 9 = 9 - 0
copy -1 = 9 - 0 - 1 - 9
length 8 -= -1 + 0

Since datalen and transhdrlen cancel, and fraggap is unsigned, if fraggap is
non-zero, copy will be negative.

> The WARN_ON_ONCE, if it can be reached, will be user triggerable.
> Usually for those cases and when there is a viable return with error
> path, that is preferable. But if you prefer to taunt syzbot, ok. We
> can always remove this later.

It shouldn't be possible for length to exceed msg->msg_iter.count (assuming
there is a msg) coming from userspace; further, userspace can't directly
specify MSG_SPLICE_PAGES.

> __ip6_append_data probably needs the same.

Good point. The arrangement of the code is a bit different, but I think it's
substantially the same in this regard.

David

\
 
 \ /
  Last update: 2023-08-01 18:58    [W:0.047 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site