[PATCH 6.1 0926/1887] rxrpc: Fix data-race warning and potential load/store tearing
Greg Kroah-Hartman
gregkh at linuxfoundation.org
Wed Oct 28 09:50:22 PDT 2026
6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: David Howells <dhowells at redhat.com>
[ Upstream commit 5d5fe8bcd331f1e34e0943ec7c18432edfcf0e8b ]
Fix the following:
BUG: KCSAN: data-race in rxrpc_peer_keepalive_worker / rxrpc_send_data_packet
which is reporting an issue with the reads and writes to ->last_tx_at in:
conn->peer->last_tx_at = ktime_get_seconds();
and:
keepalive_at = peer->last_tx_at + RXRPC_KEEPALIVE_TIME;
The lockless accesses to these to values aren't actually a problem as the
read only needs an approximate time of last transmission for the purposes
of deciding whether or not the transmission of a keepalive packet is
warranted yet.
Also, as ->last_tx_at is a 64-bit value, tearing can occur on a 32-bit
arch.
Fix both of these by switching to an unsigned int for ->last_tx_at and only
storing the LSW of the time64_t. It can then be reconstructed at need
provided no more than 68 years has elapsed since the last transmission.
Fixes: ace45bec6d77 ("rxrpc: Fix firewall route keepalive")
Reported-by: syzbot+6182afad5045e6703b3d at syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/695e7cfb.050a0220.1c677c.036b.GAE@google.com/
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: stable at kernel.org
Link: https://patch.msgid.link/1107124.1768903985@warthog.procyon.org.uk
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
net/rxrpc/ar-internal.h | 9 ++++++++-
net/rxrpc/conn_event.c | 4 ++--
net/rxrpc/output.c | 10 +++++-----
net/rxrpc/peer_event.c | 17 ++++++++++++++++-
net/rxrpc/proc.c | 4 ++--
net/rxrpc/rxkad.c | 4 ++--
6 files changed, 35 insertions(+), 13 deletions(-)
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 8499ceb7719c8..fbec55c7e6dc5 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -303,7 +303,7 @@ struct rxrpc_peer {
struct hlist_head error_targets; /* targets for net error distribution */
struct rb_root service_conns; /* Service connections */
struct list_head keepalive_link; /* Link in net->peer_keepalive[] */
- time64_t last_tx_at; /* Last time packet sent here */
+ unsigned int last_tx_at; /* Last time packet sent here (time64_t LSW) */
seqlock_t service_conn_lock;
spinlock_t lock; /* access lock */
unsigned int if_mtu; /* interface MTU for this peer */
@@ -986,6 +986,13 @@ void rxrpc_encap_err_rcv(struct sock *sk, struct sk_buff *skb, unsigned int udp_
void rxrpc_error_report(struct sock *);
void rxrpc_peer_keepalive_worker(struct work_struct *);
+/* Update the last transmission time on a peer for keepalive purposes. */
+static inline void rxrpc_peer_mark_tx(struct rxrpc_peer *peer)
+{
+ /* To avoid tearing on 32-bit systems, we only keep the LSW. */
+ WRITE_ONCE(peer->last_tx_at, ktime_get_seconds());
+}
+
/*
* peer_object.c
*/
diff --git a/net/rxrpc/conn_event.c b/net/rxrpc/conn_event.c
index 293922df2a891..8079094844c0e 100644
--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -142,7 +142,7 @@ static void rxrpc_conn_retransmit_call(struct rxrpc_connection *conn,
}
ret = kernel_sendmsg(conn->params.local->socket, &msg, iov, ioc, len);
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
if (ret < 0)
trace_rxrpc_tx_fail(chan->call_debug_id, serial, ret,
rxrpc_tx_point_call_final_resend);
@@ -262,7 +262,7 @@ static int rxrpc_abort_connection(struct rxrpc_connection *conn,
trace_rxrpc_tx_packet(conn->debug_id, &whdr, rxrpc_tx_point_conn_abort);
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
_leave(" = 0");
return 0;
diff --git a/net/rxrpc/output.c b/net/rxrpc/output.c
index 3d9032fae9d91..6fb0c67ef8bb4 100644
--- a/net/rxrpc/output.c
+++ b/net/rxrpc/output.c
@@ -254,7 +254,7 @@ int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
rtt_slot = rxrpc_begin_rtt_probe(call, serial, rxrpc_rtt_tx_ping);
ret = kernel_sendmsg(conn->params.local->socket, &msg, iov, 2, len);
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
if (ret < 0)
trace_rxrpc_tx_fail(call->debug_id, serial, ret,
rxrpc_tx_point_call_ack);
@@ -333,7 +333,7 @@ int rxrpc_send_abort_packet(struct rxrpc_call *call)
ret = kernel_sendmsg(conn->params.local->socket,
&msg, iov, 1, sizeof(pkt));
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
if (ret < 0)
trace_rxrpc_tx_fail(call->debug_id, serial, ret,
rxrpc_tx_point_call_abort);
@@ -449,7 +449,7 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb,
* message and update the peer record
*/
ret = kernel_sendmsg(conn->params.local->socket, &msg, iov, 2, len);
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
up_read(&conn->params.local->defrag_sem);
if (ret < 0) {
@@ -525,7 +525,7 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb,
IP_PMTUDISC_DONT);
ret = kernel_sendmsg(conn->params.local->socket, &msg,
iov, 2, len);
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
ip_sock_set_mtu_discover(conn->params.local->socket->sk,
IP_PMTUDISC_DO);
@@ -674,6 +674,6 @@ void rxrpc_send_keepalive(struct rxrpc_peer *peer)
trace_rxrpc_tx_packet(peer->debug_id, &whdr,
rxrpc_tx_point_version_keepalive);
- peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(peer);
_leave("");
}
diff --git a/net/rxrpc/peer_event.c b/net/rxrpc/peer_event.c
index 32561e9567fe3..77005c97dd904 100644
--- a/net/rxrpc/peer_event.c
+++ b/net/rxrpc/peer_event.c
@@ -515,6 +515,21 @@ static void rxrpc_distribute_error(struct rxrpc_peer *peer, int error,
}
}
+/*
+ * Reconstruct the last transmission time. The difference calculated should be
+ * valid provided no more than ~68 years elapsed since the last transmission.
+ */
+static time64_t rxrpc_peer_get_tx_mark(const struct rxrpc_peer *peer, time64_t base)
+{
+ s32 last_tx_at = READ_ONCE(peer->last_tx_at);
+ s32 base_lsw = base;
+ s32 diff = last_tx_at - base_lsw;
+
+ diff = clamp(diff, -RXRPC_KEEPALIVE_TIME, RXRPC_KEEPALIVE_TIME);
+
+ return diff + base;
+}
+
/*
* Perform keep-alive pings.
*/
@@ -541,7 +556,7 @@ static void rxrpc_peer_keepalive_dispatch(struct rxrpc_net *rxnet,
if (__rxrpc_use_local(peer->local)) {
spin_unlock_bh(&rxnet->peer_hash_lock);
- keepalive_at = peer->last_tx_at + RXRPC_KEEPALIVE_TIME;
+ keepalive_at = rxrpc_peer_get_tx_mark(peer, base) + RXRPC_KEEPALIVE_TIME;
slot = keepalive_at - base;
_debug("%02x peer %u t=%d {%pISp}",
cursor, peer->debug_id, slot, &peer->srx.transport);
diff --git a/net/rxrpc/proc.c b/net/rxrpc/proc.c
index 47d36554ad311..ee07785860a01 100644
--- a/net/rxrpc/proc.c
+++ b/net/rxrpc/proc.c
@@ -234,13 +234,13 @@ static int rxrpc_peer_seq_show(struct seq_file *seq, void *v)
now = ktime_get_seconds();
seq_printf(seq,
"UDP %-47.47s %-47.47s %3u"
- " %3u %5u %6llus %8u %8u\n",
+ " %3u %5u %6ds %8u %8u\n",
lbuff,
rbuff,
refcount_read(&peer->ref),
peer->cong_cwnd,
peer->mtu,
- now - peer->last_tx_at,
+ (s32)now - (s32)READ_ONCE(peer->last_tx_at),
peer->srtt_us >> 3,
jiffies_to_usecs(peer->rto_j));
diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index 84a61fa18bc06..038c4f2e8cef8 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -780,7 +780,7 @@ static int rxkad_issue_challenge(struct rxrpc_connection *conn)
return -EAGAIN;
}
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
trace_rxrpc_tx_packet(conn->debug_id, &whdr,
rxrpc_tx_point_rxkad_challenge);
_leave(" = 0");
@@ -838,7 +838,7 @@ static int rxkad_send_response(struct rxrpc_connection *conn,
return -EAGAIN;
}
- conn->params.peer->last_tx_at = ktime_get_seconds();
+ rxrpc_peer_mark_tx(conn->params.peer);
_leave(" = 0");
return 0;
}
--
2.53.0
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