linux-kernel - [PATCH] RDMA/ocrdma: Fix an off-by-one issue in 'ocrdma_add

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Date:   Sat, 28 Mar 2020 08:30:40 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     selvin.xavier@...adcom.com, devesh.sharma@...adcom.com,
        dledford@...hat.com, jgg@...pe.ca, leon@...nel.org,
        colin.king@...onical.com, roland@...estorage.com
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] RDMA/ocrdma: Fix an off-by-one issue in 'ocrdma_add_stat'

There is an off-by-one issue when checking if there is enough space in the
output buffer, because we must keep some place for a final '\0'.

While at it:
   - Use 'scnprintf' instead of 'snprintf' in order to avoid a superfluous
    'strlen'
   - avoid some useless initializations
   - avoida hard coded buffer size that can be computed at built time.

Fixes: a51f06e1679e ("RDMA/ocrdma: Query controller information")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
The '\0' comes from memset(..., 0, ...) in all callers.
This could be also avoided if needed.
---
 drivers/infiniband/hw/ocrdma/ocrdma_stats.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/ocrdma/ocrdma_stats.c b/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
index 5f831e3bdbad..614a449e6b87 100644
--- a/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
+++ b/drivers/infiniband/hw/ocrdma/ocrdma_stats.c
@@ -49,13 +49,12 @@ static struct dentry *ocrdma_dbgfs_dir;
 static int ocrdma_add_stat(char *start, char *pcur,
 				char *name, u64 count)
 {
-	char buff[128] = {0};
-	int cpy_len = 0;
+	char buff[128];
+	int cpy_len;
 
-	snprintf(buff, 128, "%s: %llu\n", name, count);
-	cpy_len = strlen(buff);
+	cpy_len = scnprintf(buff, sizeof(buff), "%s: %llu\n", name, count);
 
-	if (pcur + cpy_len > start + OCRDMA_MAX_DBGFS_MEM) {
+	if (pcur + cpy_len >= start + OCRDMA_MAX_DBGFS_MEM) {
 		pr_err("%s: No space in stats buff\n", __func__);
 		return 0;
 	}
-- 
2.20.1