libbb/yescrypt: code shrink in salt decoding

function                                             old     new   delta
yescrypt_r                                          1311    1288     -23

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 11 insertions, 15 deletions

diff --git a/libbb/yescrypt/alg-yescrypt-common.c b/libbb/yescrypt/alg-yescrypt-common.c
index 65c92f22f..8d75fa051 100644
--- a/libbb/yescrypt/alg-yescrypt-common.c
+++ b/libbb/yescrypt/alg-yescrypt-common.c
@@ -233,33 +233,29 @@ uint8_t *yescrypt_r(
         }
         if (!src)
                 return NULL;
-        if (*src++ != '$')
+        if (*src != '$')
                 return NULL;
 
-        prefixlen = src - setting;
-
-        saltstr = src;
-        src = (uint8_t *)strrchr((char *)saltstr, '$');
-        if (src)
-                saltstrlen = src - saltstr;
-        else
-                saltstrlen = strlen((char *)saltstr);
+        saltstr = src + 1;
+        src = (uint8_t *)strchrnul((char *)saltstr, '$');
+        prefixlen = src - setting;  /* len("$y$<params>$<salt>") */
+        saltstrlen = src - saltstr; /* len("<salt>") */
+        /* src points to end of salt ('$' or NUL byte), won't be used past this point */
 
         saltlen = sizeof(saltbin);
         saltend = decode64(saltbin, &saltlen, saltstr, saltstrlen);
+        if (saltend != saltstr + saltstrlen)
+                goto fail; /* saltbin[] is too small, or bad char during decode */
 
-        if (!saltend || (size_t)(saltend - saltstr) != saltstrlen)
-                goto fail;
-
-        need = prefixlen + saltstrlen + 1 + HASH_LEN + 1;
-        if (need > buflen || need < saltstrlen)
+        need = prefixlen + 1 + HASH_LEN + 1;
+        if (need > buflen || need < prefixlen)
                 goto fail;
 
         if (yescrypt_kdf(local, passwd, passwdlen, saltbin, saltlen,
             &params, hashbin, sizeof(hashbin)))
                 goto fail;
 
-        dst = mempcpy(buf, setting, prefixlen + saltstrlen);
+        dst = mempcpy(buf, setting, prefixlen);
         *dst++ = '$';
         dst = encode64(dst, buflen - (dst - buf), hashbin, sizeof(hashbin));
         explicit_bzero(hashbin, sizeof(hashbin));