Flags passed in for splice() syscall should not end up in skb_recv_datagram(). As SPLICE_F_NONBLOCK == MSG_PEEK, kernel gets confused: skb isn't unlinked from a receive queue, while strp_msg::offset and strp_msg::full_len are updated. Unbreak the logic a bit more by mapping both O_NONBLOCK and SPLICE_F_NONBLOCK to MSG_DONTWAIT. This way we align with man splice(2) in regard to errno EAGAIN: SPLICE_F_NONBLOCK was specified in flags or one of the file descriptors had been marked as nonblocking (O_NONBLOCK), and the operation would block. Fixes: 5121197ecc5d ("kcm: close race conditions on sk_receive_queue") Fixes: 91687355b927 ("kcm: Splice support") Signed-off-by: Michal Luczaj --- net/kcm/kcmsock.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c index 24aec295a51cf737912f1aefe81556bd9f23331e..c05047dad62d7e201c950ab98af6dc7f0d48276c 100644 --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include #include @@ -1030,6 +1031,11 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos, ssize_t copied; struct sk_buff *skb; + if (sock->file->f_flags & O_NONBLOCK || flags & SPLICE_F_NONBLOCK) + flags = MSG_DONTWAIT; + else + flags = 0; + /* Only support splice for SOCKSEQPACKET */ skb = skb_recv_datagram(sk, flags, &err); --- base-commit: c8f13134349b4385ae739f1efe403d5d3949ef92 change-id: 20250619-kcm-splice-01cb39a5997b Best regards, -- Michal Luczaj