netdev - [PATCH net] tipc: use a write lock for keepalive

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Date:   Tue, 29 Mar 2022 18:12:14 +0200
From:   Niels Dossche <dossche.niels@...il.com>
To:     tipc-discussion@...ts.sourceforge.net
Cc:     netdev@...r.kernel.org, Jon Maloy <jmaloy@...hat.com>,
        Ying Xue <ying.xue@...driver.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hoang Le <hoang.h.le@...tech.com.au>,
        Niels Dossche <dossche.niels@...il.com>
Subject: [PATCH net] tipc: use a write lock for keepalive_intv instead of a read lock

Currently, n->keepalive_intv is written to while n is locked by a read
lock instead of a write lock. This seems to me to break the atomicity
against other readers.
Change this to a write lock instead to solve the issue.

Note:
I am currently working on a static analyser to detect missing locks
using type-based static analysis as my master's thesis
in order to obtain my master's degree.
If you would like to have more details, please let me know.
This was a reported case. I manually verified the report by looking
at the code, so that I do not send wrong information or patches.
After concluding that this seems to be a true positive, I created
this patch. I have both compile-tested this patch and runtime-tested
this patch on x86_64. The effect on a running system could be a
potential race condition in exceptional cases.
This issue was found on Linux v5.17.

Fixes: f5d6c3e5a359 ("tipc: fix node keep alive interval calculation")
Signed-off-by: Niels Dossche <dossche.niels@...il.com>
---
 net/tipc/node.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 6ef95ce565bd..da867ddb93f5 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -806,9 +806,9 @@ static void tipc_node_timeout(struct timer_list *t)
 	/* Initial node interval to value larger (10 seconds), then it will be
 	 * recalculated with link lowest tolerance
 	 */
-	tipc_node_read_lock(n);
+	tipc_node_write_lock(n);
 	n->keepalive_intv = 10000;
-	tipc_node_read_unlock(n);
+	tipc_node_write_unlock(n);
 	for (bearer_id = 0; remains && (bearer_id < MAX_BEARERS); bearer_id++) {
 		tipc_node_read_lock(n);
 		le = &n->links[bearer_id];
-- 
2.35.1