[PATCH] io_uring/net: keep recvmsg buffer select length within MAX_RW_COUNT

[PATCH] io_uring/net: keep recvmsg buffer select length within MAX_RW_COUNT

[Yichong Chen]

io_recvmsg() takes the transfer length from the ring provided buffer when
sqe->len is 0, and such a buffer can be up to 4G. min_ret is an int, so 2G
or more makes it negative and the (ret < min_ret) block is skipped, and the
oversized length reaches the socket layer unchanged: an empty socket then
completes with 0 instead of arming poll, and a short read is reported as
complete. Clamp the length to MAX_RW_COUNT, as io_recv() does.

Fixes: 78d0d2063bab ("io_uring/net: disable partial retries for recvmsg with cmsg")
Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
---
 io_uring/net.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/io_uring/net.c b/io_uring/net.c
index eeab88e77fd8..4678f29f5177 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -1068,6 +1068,7 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
 		sel = io_buffer_select(req, &len, sr->buf_group, issue_flags);
 		if (!sel.addr)
 			return -ENOBUFS;
+		len = min_t(size_t, len, MAX_RW_COUNT);
 
 		if (req->flags & REQ_F_APOLL_MULTISHOT) {
 			ret = io_recvmsg_prep_multishot(kmsg, sr, &sel.addr, &len);
-- 
2.51.0

Re: [PATCH] io_uring/net: keep recvmsg buffer select length within MAX_RW_COUNT

[Jens Axboe]

On 10/23/26 5:22 AM, Yichong Chen wrote:
> io_recvmsg() takes the transfer length from the ring provided buffer when
> sqe->len is 0, and such a buffer can be up to 4G. min_ret is an int, so 2G
> or more makes it negative and the (ret < min_ret) block is skipped, and the
> oversized length reaches the socket layer unchanged: an empty socket then
> completes with 0 instead of arming poll, and a short read is reported as
> complete. Clamp the length to MAX_RW_COUNT, as io_recv() does.
> 
> Fixes: 78d0d2063bab ("io_uring/net: disable partial retries for recvmsg with cmsg")

Don't think that's correct, it just moved the check. Should be:

c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")

instead. I will fix that up. Waiting on Linus pulling the
previous bits, then I will queue this up for 7.4.

-- 
Jens Axboe