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Starke" To: linux-serial@vger.kernel.org, gregkh@linuxfoundation.org, jirislaby@kernel.org, ilpo.jarvinen@linux.intel.com Cc: linux-kernel@vger.kernel.org, Daniel Starke Subject: [PATCH 1/2] tty: n_gsm: fix race condition in status line change on dead connections Date: Thu, 26 Oct 2023 07:58:43 +0200 Message-Id: <20231026055844.3127-1-daniel.starke@siemens.com> MIME-Version: 1.0 X-Flowmailer-Platform: Siemens Feedback-ID: 519:519-314044:519-21489:flowmailer X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on howler.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (howler.vger.email [0.0.0.0]); Wed, 25 Oct 2023 23:01:29 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1780796718612609853 X-GMAIL-MSGID: 1780796718612609853 From: Daniel Starke gsm_cleanup_mux() cleans up the gsm by closing all DLCIs, stopping all timers, removing the virtual tty devices and clearing the data queues. This procedure, however, may cause subsequent changes of the virtual modem status lines of a DLCI. More data is being added the outgoing data queue and the deleted kick timer is restarted to handle this. At this point many resources have already been removed by the cleanup procedure. Thus, a kernel panic occurs. Fix this by proving in gsm_modem_update() that the cleanup procedure has not been started and the mux is still alive. Note that writing to a virtual tty is already protected by checks against the DLCI specific connection state. Fixes: c568f7086c6e ("tty: n_gsm: fix missing timer to handle stalled links") Signed-off-by: Daniel Starke --- drivers/tty/n_gsm.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 1f3aba607cd5..0ee7531c9201 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -4108,6 +4108,8 @@ static int gsm_modem_upd_via_msc(struct gsm_dlci *dlci, u8 brk) static int gsm_modem_update(struct gsm_dlci *dlci, u8 brk) { + if (dlci->gsm->dead) + return -EL2HLT; if (dlci->adaption == 2) { /* Send convergence layer type 2 empty data frame. */ gsm_modem_upd_via_data(dlci, brk);