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io_uring/net: fix fast_iov assignment in io_setup_async_msg() 

commit 3e4cb6ebbb upstream.

I hit a very bad problem during my tests of SENDMSG_ZC.
BUG(); in first_iovec_segment() triggered very easily.
The problem was io_setup_async_msg() in the partial retry case,
which seems to happen more often with _ZC.

iov_iter_iovec_advance() may change i->iov in order to have i->iov_offset
being only relative to the first element.

Which means kmsg->msg.msg_iter.iov is no longer the
same as kmsg->fast_iov.

But this would rewind the copy to be the start of
async_msg->fast_iov, which means the internal
state of sync_msg->msg.msg_iter is inconsitent.

I tested with 5 vectors with length like this 4, 0, 64, 20, 8388608
and got a short writes with:
- ret=2675244 min_ret=8388692 => remaining 5713448 sr->done_io=2675244
- ret=-EAGAIN => io_uring_poll_arm
- ret=4911225 min_ret=5713448 => remaining 802223  sr->done_io=7586469
- ret=-EAGAIN => io_uring_poll_arm
- ret=802223  min_ret=802223  => res=8388692

While this was easily triggered with SENDMSG_ZC (queued for 6.1),
it was a potential problem starting with 7ba89d2af1
in 5.18 for IORING_OP_RECVMSG.
And also with 4c3c09439c in 5.19
for IORING_OP_SENDMSG.

However 257e84a537 introduced the critical
code into io_setup_async_msg() in 5.11.

Fixes: 7ba89d2af1 ("io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly")
Fixes: 257e84a537 ("io_uring: refactor sendmsg/recvmsg iov managing")
Cc: stable@vger.kernel.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b2e7be246e2fb173520862b0c7098e55767567a2.1664436949.git.metze@samba.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Stefan Metzmacher 2022-09-29 09:39:10 +02:00 committed by Greg Kroah-Hartman
parent 89a77271d2
commit fc2491562a
1 changed files with 4 additions and 2 deletions
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6
io_uring/io_uring.c
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@ -4681,8 +4681,10 @@ static int io_setup_async_msg(struct io_kiocb *req,
if (async_msg->msg.msg_name)
async_msg->msg.msg_name = &async_msg->addr;
/* if were using fast_iov, set it to the new one */
if (!async_msg->free_iov)
async_msg->msg.msg_iter.iov = async_msg->fast_iov;
if (!kmsg->free_iov) {
size_t fast_idx = kmsg->msg.msg_iter.iov - kmsg->fast_iov;
async_msg->msg.msg_iter.iov = &async_msg->fast_iov[fast_idx];
}
return -EAGAIN;
}