Replace strlen-then-snprintf pattern in save_serial() with a single truncation check.

This used to be necessary because BIO_snprintf() could not detect truncation
but now this is silly, and this ends up tripping GCC's -Wformat-truncation

Reviewed-by: Neil Horman <[email protected]>
Reviewed-by: Andrew Dinh <[email protected]>
MergeDate: Wed Aug 26 16:20:30 2026
(Merged from https://github.com/openssl/openssl/pull/31640)

1 files changed, 13 insertions, 13 deletions

diff --git a/apps/lib/apps.c b/apps/lib/apps.c
index 5159e325cc2..14b6d6d8145 100644
--- a/apps/lib/apps.c
+++ b/apps/lib/apps.c
@@ -1745,25 +1745,25 @@ int save_serial(const char *serialfile, const char *suffix,
     BIO *out = NULL;
     int ret = 0;
     ASN1_INTEGER *ai = NULL;
-    size_t j;
-
-    if (suffix == NULL)
-        j = strlen(serialfile);
-    else
-        j = strlen(serialfile) + strlen(suffix) + 1;
-    if (j >= BSIZE) {
-        BIO_puts(bio_err, "File name too long\n");
-        goto err;
-    }
 
     if (suffix == NULL) {
-        OPENSSL_strlcpy(buf[0], serialfile, BSIZE);
+        if (OPENSSL_strlcpy(buf[0], serialfile, BSIZE) >= BSIZE) {
+            BIO_puts(bio_err, "File name too long\n");
+            goto err;
+        }
     } else {
+        int n = snprintf(buf[0], sizeof(buf[0]),
 #ifndef OPENSSL_SYS_VMS
-        snprintf(buf[0], sizeof(buf[0]), "%s.%s", serialfile, suffix);
+            "%s.%s",
 #else
-        snprintf(buf[0], sizeof(buf[0]), "%s-%s", serialfile, suffix);
+            "%s-%s",
 #endif
+            serialfile, suffix);
+
+        if (n < 0 || (size_t)n >= sizeof(buf[0])) {
+            BIO_puts(bio_err, "File name too long\n");
+            goto err;
+        }
     }
     out = BIO_new_file(buf[0], "w");
     if (out == NULL) {