[PATCH] lpfc: Fix less-than-zero comparison of unsigned value

[PATCH] lpfc: Fix less-than-zero comparison of unsigned value

[James Smart]

The expressions start_idx - dbg_cnt is evaluated using unsigned int
arthithmetic (since these variables are unsigned ints) and hence can
never be less than zero, so the less than comparison is never true.
Re-write the expression to check for start_idx being less than dbg_cnt.

After the logic was corrected, temp_idx wasn't working correct. So fix it
was fixed as well.

Addresses-Coverity: ("Unsigned compared against 0")
Fixes: 372c187b8a70 ("scsi: lpfc: Add an internal trace log buffer")
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
CC: Colin Ian King <colin.king@canonical.com>
---
 drivers/scsi/lpfc/lpfc_init.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/lpfc/lpfc_init.c b/drivers/scsi/lpfc/lpfc_init.c
index 4ba8202d391b..f3656bdcb582 100644
--- a/drivers/scsi/lpfc/lpfc_init.c
+++ b/drivers/scsi/lpfc/lpfc_init.c
@@ -14161,12 +14161,10 @@ void lpfc_dmp_dbg(struct lpfc_hba *phba)
 		if ((start_idx + dbg_cnt) > (DBG_LOG_SZ - 1)) {
 			temp_idx = (start_idx + dbg_cnt) % DBG_LOG_SZ;
 		} else {
-			if ((start_idx - dbg_cnt) < 0) {
+			if (start_idx < dbg_cnt)
 				start_idx = DBG_LOG_SZ - (dbg_cnt - start_idx);
-				temp_idx = 0;
-			} else {
+			else
 				start_idx -= dbg_cnt;
-			}
 		}
 	}
 	dev_info(&phba->pcidev->dev, "start %d end %d cnt %d\n",
@@ -14174,7 +14172,7 @@ void lpfc_dmp_dbg(struct lpfc_hba *phba)
 
 	for (i = 0; i < dbg_cnt; i++) {
 		if ((start_idx + i) < DBG_LOG_SZ)
-			temp_idx = (start_idx + i) % (DBG_LOG_SZ - 1);
+			temp_idx = (start_idx + i) % DBG_LOG_SZ;
 		else
 			temp_idx = j++;
 		rem_nsec = do_div(phba->dbg_log[temp_idx].t_ns, NSEC_PER_SEC);
-- 
2.25.0

Re: [PATCH] lpfc: Fix less-than-zero comparison of unsigned value

[Martin K. Petersen]

On Mon, 6 Jul 2020 13:42:46 -0700, James Smart wrote:

> The expressions start_idx - dbg_cnt is evaluated using unsigned int
> arthithmetic (since these variables are unsigned ints) and hence can
> never be less than zero, so the less than comparison is never true.
> Re-write the expression to check for start_idx being less than dbg_cnt.
> 
> After the logic was corrected, temp_idx wasn't working correct. So fix it
> was fixed as well.

Applied to 5.9/scsi-queue, thanks!

[1/1] scsi: lpfc: Fix less-than-zero comparison of unsigned value
      https://git.kernel.org/mkp/scsi/c/77dd7d7b3442

-- 
Martin K. Petersen	Oracle Linux Engineering