Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> 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
