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([2a09:bac6:37a8:26dc::3df:8]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45eaa93cea9sm2582382f8f.35.2026.05.21.06.06.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2026 06:06:30 -0700 (PDT) From: Matt Fleming To: Corey Minyard Cc: Gilles BULOZ , kernel-team@cloudflare.com, Matt Fleming , stable@vger.kernel.org, openipmi-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: [PATCH] ipmi: Fix user refcount underflow in event delivery Date: Thu, 21 May 2026 14:06:27 +0100 Message-ID: <20260521130628.3641050-1-matt@readmodwrite.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Matt Fleming ipmi_alloc_recv_msg(user) takes the temporary user reference owned by the receive message, and ipmi_free_recv_msg() drops it again. If event delivery fails after allocating receive messages for earlier users, handle_read_event_rsp() rolls those messages back with ipmi_free_recv_msg(). That rollback path still drops user->refcount explicitly after freeing each message. The extra put can free a user that remains linked on intf->users, so later event delivery may dereference a freed user or trip refcount_t's addition-on-zero warning when ipmi_alloc_recv_msg() tries to acquire another reference. Remove the stale explicit put and the now-dead user assignment. Keep the list_del() and ipmi_free_recv_msg() calls; they are the required rollback operations. Fixes: b52da4054ee0 ("ipmi: Rework user message limit handling") Cc: stable@vger.kernel.org Signed-off-by: Matt Fleming --- drivers/char/ipmi/ipmi_msghandler.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_m= sghandler.c index 869ac87a4b6a..52561a880e54 100644 --- a/drivers/char/ipmi/ipmi_msghandler.c +++ b/drivers/char/ipmi/ipmi_msghandler.c @@ -4477,10 +4477,8 @@ static int handle_read_event_rsp(struct ipmi_smi *in= tf, mutex_unlock(&intf->users_mutex); list_for_each_entry_safe(recv_msg, recv_msg2, &msgs, link) { - user =3D recv_msg->user; list_del(&recv_msg->link); ipmi_free_recv_msg(recv_msg); - kref_put(&user->refcount, free_ipmi_user); } /* * We couldn't allocate memory for the --=20 2.43.0