This change should cause no difference in behavior; it just cleans up some hazardous code that could have become a problem in the future. MSG_NO_SHARED_FRAGS is a kernel-internal flag that cancels the effect of MSG_SPLICE_PAGES, another kernel-internal flag that influences the data-sharing semantics of SKBs. Prevent passing this flag in from userspace via sendmsg() by adding it to MSG_INTERNAL_SENDMSG_FLAGS. This is not currently an observable problem because MSG_NO_SHARED_FRAGS only has an effect if kernel code adds MSG_SPLICE_PAGES to it. The only codepath that adds MSG_SPLICE_PAGES to user-supplied flags from which MSG_NO_SHARED_FRAGS hasn't been cleared is the path tcp_bpf_sendmsg -> tcp_bpf_send_verdict -> tcp_bpf_push, and that is not a problem because tcp_bpf_sendmsg always intentionally sets MSG_NO_SHARED_FRAGS anyway. Signed-off-by: Jann Horn --- include/linux/socket.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/socket.h b/include/linux/socket.h index ec4a0a025793..1a4d0d128a13 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -357,7 +357,7 @@ struct ucred { /* Flags to be cleared on entry by sendmsg and sendmmsg syscalls */ #define MSG_INTERNAL_SENDMSG_FLAGS \ - (MSG_SPLICE_PAGES | MSG_SENDPAGE_NOPOLICY | MSG_SENDPAGE_DECRYPTED) + (MSG_SPLICE_PAGES | MSG_SENDPAGE_NOPOLICY | MSG_SENDPAGE_DECRYPTED | MSG_NO_SHARED_FRAGS) /* Setsockoptions(2) level. Thanks to BSD these must match IPPROTO_xxx */ #define SOL_IP 0 --- base-commit: 5d6919055dec134de3c40167a490f33c74c12581 change-id: 20260511-msg_no_shared_frags-d557c14e487b -- Jann Horn