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| author | Jann Horn <jannh@google.com> | 2026-05-12 16:02:03 +0200 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-05-14 18:00:40 -0700 |
| commit | 4987a5763fd5ab72afde7493216d944d976a0b15 (patch) | |
| tree | f9998e3b5a5cf543b8ef92933418f2fac7db8747 /include/linux | |
| parent | e54fe8200a1c72c624846d22ad9c2820f8ab06c3 (diff) | |
| download | lwn-4987a5763fd5ab72afde7493216d944d976a0b15.tar.gz lwn-4987a5763fd5ab72afde7493216d944d976a0b15.zip | |
net: block MSG_NO_SHARED_FRAGS in sendmsg()
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 <jannh@google.com>
Link: https://patch.msgid.link/20260512-msg_no_shared_frags-v1-1-55ea46760331@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/socket.h | 2 |
1 files changed, 1 insertions, 1 deletions
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 |