From: Stefan Metzmacher metze@samba.org
commit 3e4cb6ebbb2bad201c1186bc0b7e8cf41dd7f7e6 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 7ba89d2af17aa879dda30f5d5d3f152e587fc551 in 5.18 for IORING_OP_RECVMSG. And also with 4c3c09439c08b03d9503df0ca4c7619c5842892e in 5.19 for IORING_OP_SENDMSG.
However 257e84a5377fbbc336ff563833a8712619acce56 introduced the critical code into io_setup_async_msg() in 5.11.
Fixes: 7ba89d2af17aa ("io_uring: ensure recv and recvmsg handle MSG_WAITALL correctly") Fixes: 257e84a5377fb ("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/b2e7be246e2fb173520862b0c7098e55767567a2.166443694... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/io_uring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -4681,8 +4681,10 @@ static int io_setup_async_msg(struct io_ 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; }