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Thu, 3 Sep 2026 13:07:34 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 3 Sep 2026 13:07:34 +0000 (GMT) From: Mikhail Zaslonko To: linux-s390@vger.kernel.org Cc: Heiko Carstens , Alexander Gordeev , Vasily Gorbik , Ilya Leoshkevich , Peter Oberparleiter Subject: [PATCH v3 3/3] s390/debug: Fix race between debug area resize and event logging Date: Thu, 3 Sep 2026 15:07:33 +0200 Message-ID: <20260903130733.709001-4-zaslonko@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260903130733.709001-1-zaslonko@linux.ibm.com> References: <20260903130733.709001-1-zaslonko@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: ITBxHuFoQ5BB6Ghp1BDFernTzurzl6zA X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAzMDExMyBTYWx0ZWRfX3FzuT9u1STKA XZlbtzKheKfCgphd5M6InXHvjia8EjExRnY+tbF/XtB81CSBwhQPz5/MxckmVyrJqdAAfQMS1Rp UPS5bHRGmUrkrabkmm+SlJ5GAA1frQWmywWlxDv6/ZK9F2MDX/65RI4KtJNaveV9mCz7oOuOdKr ZxBCOpINo3913dkbVLdto4QFM6GP5ePG3p9P+g/pxEIeskDjvw2vBslw3LD4mgcjZrsGwhNh2ql tJyPrG9O3ReZUYzQXQkalbfm+fMTsXwvJJxzZaRwDNLV7S3BOEhKVq44w6D0wQR9qRGHrGc6KFh zxcQj/duqCCOF8/9X1WgKIfq72WR0xV6eZQhiimoHim/lTcFSde4kx+uloeIcI/1U56UQ72100r SHf4OTNETpuFXG4LJWPzP/il7LoQnrXGVZdmNpBjyQUc/ah99cjStCrF2JgXvfDMc1wAJEWFToA ryW7uoJ7wAhUoHhSuCg== X-Proofpoint-ORIG-GUID: ITBxHuFoQ5BB6Ghp1BDFernTzurzl6zA X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAzMDExMyBTYWx0ZWRfX/+ujYW4LAkkK GzEqWR09P3eKIRcmqToGffhN9DdfnmA9vXNXddZOvoT2b8oG2xqYWkc0bixXgGwVMs5FNgeENWT gBlfCMQIKlF83TJWjuGudBCmBnQpUUY= X-Authority-Analysis: v=2.4 cv=B92JFutM c=1 sm=1 tr=0 ts=6a99711b cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=sHLu9uPjF0jMMvyWv9sA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-03_03,2026-09-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 spamscore=0 clxscore=1015 suspectscore=0 phishscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609030113 Trace functions check for non-NULL id->areas without lock to minimize overhead. This opens a race window where a NULL pointer dereference occurs if id->areas is set to NULL (e.g. via echo 0 > ../pages) after the check and before id->lock is taken. Fix this by rechecking id->areas under lock. Signed-off-by: Mikhail Zaslonko Reviewed-by: Peter Oberparleiter --- arch/s390/kernel/debug.c | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-) diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c index cf411f203571..b5bf8284dbfc 100644 --- a/arch/s390/kernel/debug.c +++ b/arch/s390/kernel/debug.c @@ -1283,7 +1283,7 @@ void debug_set_critical(void) debug_entry_t *debug_event_common(debug_info_t *id, int level, const void *buf, int len) { - debug_entry_t *active; + debug_entry_t *active = NULL; unsigned long flags; if (!debug_active || !id->areas) @@ -1294,6 +1294,8 @@ debug_entry_t *debug_event_common(debug_info_t *id, int level, const void *buf, } else { raw_spin_lock_irqsave(&id->lock, flags); } + if (!id->areas) + goto out; do { active = get_active_entry(id); memcpy(DEBUG_DATA(active), buf, min(len, id->buf_size)); @@ -1303,7 +1305,7 @@ debug_entry_t *debug_event_common(debug_info_t *id, int level, const void *buf, len -= id->buf_size; buf += id->buf_size; } while (len > 0); - +out: raw_spin_unlock_irqrestore(&id->lock, flags); return active; } @@ -1316,7 +1318,7 @@ EXPORT_SYMBOL(debug_event_common); debug_entry_t *debug_exception_common(debug_info_t *id, int level, const void *buf, int len) { - debug_entry_t *active; + debug_entry_t *active = NULL; unsigned long flags; if (!debug_active || !id->areas) @@ -1327,6 +1329,8 @@ debug_entry_t *debug_exception_common(debug_info_t *id, int level, } else { raw_spin_lock_irqsave(&id->lock, flags); } + if (!id->areas) + goto out; do { active = get_active_entry(id); memcpy(DEBUG_DATA(active), buf, min(len, id->buf_size)); @@ -1336,7 +1340,7 @@ debug_entry_t *debug_exception_common(debug_info_t *id, int level, len -= id->buf_size; buf += id->buf_size; } while (len > 0); - +out: raw_spin_unlock_irqrestore(&id->lock, flags); return active; } @@ -1362,7 +1366,7 @@ static inline int debug_count_numargs(char *string) debug_entry_t *__debug_sprintf_event(debug_info_t *id, int level, char *string, ...) { debug_sprintf_entry_t *curr_event; - debug_entry_t *active; + debug_entry_t *active = NULL; unsigned long flags; int numargs, idx; va_list ap; @@ -1377,6 +1381,8 @@ debug_entry_t *__debug_sprintf_event(debug_info_t *id, int level, char *string, } else { raw_spin_lock_irqsave(&id->lock, flags); } + if (!id->areas) + goto out; active = get_active_entry(id); curr_event = (debug_sprintf_entry_t *) DEBUG_DATA(active); va_start(ap, string); @@ -1385,6 +1391,7 @@ debug_entry_t *__debug_sprintf_event(debug_info_t *id, int level, char *string, curr_event->args[idx] = va_arg(ap, long); va_end(ap); debug_finish_entry(id, active, level, 0); +out: raw_spin_unlock_irqrestore(&id->lock, flags); return active; @@ -1397,7 +1404,7 @@ EXPORT_SYMBOL(__debug_sprintf_event); debug_entry_t *__debug_sprintf_exception(debug_info_t *id, int level, char *string, ...) { debug_sprintf_entry_t *curr_event; - debug_entry_t *active; + debug_entry_t *active = NULL; unsigned long flags; int numargs, idx; va_list ap; @@ -1413,6 +1420,8 @@ debug_entry_t *__debug_sprintf_exception(debug_info_t *id, int level, char *stri } else { raw_spin_lock_irqsave(&id->lock, flags); } + if (!id->areas) + goto out; active = get_active_entry(id); curr_event = (debug_sprintf_entry_t *)DEBUG_DATA(active); va_start(ap, string); @@ -1421,6 +1430,7 @@ debug_entry_t *__debug_sprintf_exception(debug_info_t *id, int level, char *stri curr_event->args[idx] = va_arg(ap, long); va_end(ap); debug_finish_entry(id, active, level, 1); +out: raw_spin_unlock_irqrestore(&id->lock, flags); return active; @@ -1663,9 +1673,11 @@ static void debug_flush(debug_info_t *id, int area) unsigned long flags; int i, j; - if (!id || !id->areas) + if (!id) return; raw_spin_lock_irqsave(&id->lock, flags); + if (!id->areas) + goto out; if (area == DEBUG_FLUSH_ALL) { id->active_area = 0; memset(id->active_entries, 0, id->nr_areas * sizeof(int)); @@ -1680,6 +1692,7 @@ static void debug_flush(debug_info_t *id, int area) for (i = 0; i < id->pages_per_area; i++) memset(id->areas[area][i], 0, PAGE_SIZE); } +out: raw_spin_unlock_irqrestore(&id->lock, flags); } -- 2.55.0