From 0945285e6cd67ee87e9313fb10221aba5bd69c6a Mon Sep 17 00:00:00 2001 From: Mikhail Zaslonko Date: Thu, 3 Sep 2026 15:07:33 +0200 Subject: s390/debug: Fix race between debug area resize and event logging 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 Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik --- 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); } -- cgit v1.2.3