[PATCH 21/28] NFS: nfsroot: Refactor root_nfs_cat() to use snprintf()

root_nfs_cat() computes the length of "dest" with strlen(), but then uses
up to two strlcat() calls to append a comma separator and "src",
rescanning "dest" each time.

In preparation for removing the deprecated strlcat() API[1], use the
already-computed length and a single snprintf() call to append the
optional comma and "src", returning -1 if the result is truncated.

Link: https://github.com/KSPP/linux/issues/370 [1]
Cc: codemender-patching+linux@google.com
Assisted-by: CoPilot:Claude-3.5-Sonnet [editor_update_file, make_kernel_build_single_file]
Signed-off-by: Bill Wendling <morbo@google.com>
---
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---
 fs/nfs/nfsroot.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/nfsroot.c b/fs/nfs/nfsroot.c
index 432612d22437..a28208414aec 100644
--- a/fs/nfs/nfsroot.c
+++ b/fs/nfs/nfsroot.c

@@ -173,12 +173,15 @@ static int __init root_nfs_cat(char *dest, const char *src,
 			       const size_t destlen)
 {
 	size_t len = strlen(dest);
+	int ret;
 
-	if (len && dest[len - 1] != ',')
-		if (strlcat(dest, ",", destlen) >= destlen)
-			return -1;
+	if (len >= destlen)
+		return -1;
 
-	if (strlcat(dest, src, destlen) >= destlen)
+	ret = snprintf(dest + len, destlen - len, "%s%s",
+		       (len && dest[len - 1] != ',') ? "," : "", src);
+
+	if (ret < 0 || ret >= destlen - len)
 		return -1;
 	return 0;
 }

-- 
2.55.0.1032.g73a4cd73de-goog