net: Drop the lock in skb_may_tx_timestamp()

[ Upstream commit 983512f3a87fd8dc4c94dfa6b596b6e57df5aad7 ]

skb_may_tx_timestamp() may acquire sock::sk_callback_lock. The lock must
not be taken in IRQ context, only softirq is okay. A few drivers receive
the timestamp via a dedicated interrupt and complete the TX timestamp
from that handler. This will lead to a deadlock if the lock is already
write-locked on the same CPU.

Taking the lock can be avoided. The socket (pointed by the skb) will
remain valid until the skb is released. The ->sk_socket and ->file
member will be set to NULL once the user closes the socket which may
happen before the timestamp arrives.
If we happen to observe the pointer while the socket is closing but
before the pointer is set to NULL then we may use it because both
pointer (and the file's cred member) are RCU freed.

Drop the lock. Use READ_ONCE() to obtain the individual pointer. Add a
matching WRITE_ONCE() where the pointer are cleared.

BUG=b/510709973
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2026-43216 in the Linux kernel.

cos-patch: security-moderate
Link: https://lore.kernel.org/all/20260205145104.iWinkXHv@linutronix.de
Fixes: b245be1f4db1a ("net-timestamp: no-payload only sysctl")
Change-Id: I587f7d3562942b1f084ab160e243eb11b85f243e
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260220183858.N4ERjFW6@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[adapted sk_set_socket() in include/net/sock.h to fix the conflict  from
 not having commit 5d6b58c932ec ("net: lockless sock_i_ino()") and the
 additional previous changes required by it.
 It comes down to just now having the lines of
    if (sock) {
            WRITE_ONCE(sk->sk_uid, SOCK_INODE(sock)->i_uid);
            WRITE_ONCE(sk->sk_ino, SOCK_INODE(sock)->i_ino);
    }
 below the changed line.
 I've tested this on a device running an nfs-root and did some
 additional network stress-testing.]
Signed-off-by: Heiko Stuebner <heiko.stuebner@cherry.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kernel CVE Triage Automation <cloud-image-kernel-cve-triage-automation@prod.google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/169324
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: Miri Amarilio <mirilio@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>