[PATCH v5 03/12] scsi: lpfc: Print rx monitor records straight into the seq_buf

[Kees Cook <kees@kernel.org>]

lpfc_rx_monitor_report() formats each record into a stack buffer, then
appends it with seq_buf_puts(), relying on seq_buf_puts() appending
nothing when a string does not fit: the debugfs output then ends at the
last whole record, and the record left out is read in full next time.
The next patch makes seq_buf_puts() copy as much as fits instead, as
seq_buf_printf() and strlcat() do.

Print each record with seq_buf_printf(), and when it does not fit, end
the string where the record began, since the reader takes the buffer up
to its NUL. This also takes the DBG_LOG_STR_SZ buffer off the stack.

Build tested ARCH=x86_64 with GCC 16.2.0, CONFIG_SCSI_LPFC=m and W=1.

Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
---
 drivers/scsi/lpfc/lpfc_sli.c | 45 +++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 18 deletions(-)

diff --git a/drivers/scsi/lpfc/lpfc_sli.c b/drivers/scsi/lpfc/lpfc_sli.c
index cfa4371169f1..a7b1ea67ed98 100644
--- a/drivers/scsi/lpfc/lpfc_sli.c
+++ b/drivers/scsi/lpfc/lpfc_sli.c
@@ -8108,7 +8108,6 @@ u32 lpfc_rx_monitor_report(struct lpfc_hba *phba,
 	spinlock_t *ring_lock = &rx_monitor->lock;
 	u32 ring_size = rx_monitor->entries;
 	u32 cnt = 0;
-	char tmp[DBG_LOG_STR_SZ] = {0};
 	bool log_to_kmsg = (!buf || !buf_len) ? true : false;
 	struct seq_buf s;
 
@@ -8133,27 +8132,37 @@ u32 lpfc_rx_monitor_report(struct lpfc_hba *phba,
 
 		/* Read out this entry's data. */
 		if (!log_to_kmsg) {
+			unsigned int len;
+
+			/* A header that did not fit leaves no room. */
+			if (seq_buf_has_overflowed(&s))
+				break;
+			len = seq_buf_used(&s);
+
+			seq_buf_printf(&s,
+				       "%03d:\t%-16llu%-16llu%-16llu%-16llu%-8llu%-8llu%-8llu%-8u%-8u%-8u%u(%u)\n",
+				       *head_idx,
+				       entry->max_bytes_per_interval,
+				       entry->cmf_bytes,
+				       entry->total_bytes,
+				       entry->rcv_bytes,
+				       entry->avg_io_latency,
+				       entry->avg_io_size,
+				       entry->max_read_cnt,
+				       entry->cmf_busy, entry->io_cnt,
+				       entry->cmf_info,
+				       entry->timer_utilization,
+				       entry->timer_interval);
+
 			/*
 			 * Drop a record whole if it does not fit, without
-			 * consuming its ring entry.
+			 * consuming its ring entry: the reader takes the
+			 * string up to its NUL.
 			 */
-			scnprintf(tmp, sizeof(tmp),
-				  "%03d:\t%-16llu%-16llu%-16llu%-16llu%-8llu%-8llu%-8llu%-8u%-8u%-8u%u(%u)\n",
-				  *head_idx,
-				  entry->max_bytes_per_interval,
-				  entry->cmf_bytes,
-				  entry->total_bytes,
-				  entry->rcv_bytes,
-				  entry->avg_io_latency,
-				  entry->avg_io_size,
-				  entry->max_read_cnt,
-				  entry->cmf_busy, entry->io_cnt,
-				  entry->cmf_info,
-				  entry->timer_utilization,
-				  entry->timer_interval);
-
-			if (seq_buf_puts(&s, tmp) < 0)
+			if (seq_buf_has_overflowed(&s)) {
+				buf[len] = '\0';
 				break;
+			}
 		} else {
 			lpfc_printf_log(phba, KERN_INFO, LOG_CGN_MGMT,
 					"4410 %02u: MBPI %llu Xmit %llu "
-- 
2.55.0