libbb: make pw_encrypt() die if supplied salt is bad (e.g. emply)

Fished from 520-loginutils-handle-crypt-failures.patch in openwrt

function                                             old     new   delta
pw_encrypt                                           913     927     +14
des_crypt                                           1327    1318      -9
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 14/-9)               Total: 5 bytes

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

1 files changed, 11 insertions, 14 deletions

diff --git a/libbb/pw_encrypt_des.c b/libbb/pw_encrypt_des.c
index c6fc328d8..dcd3521e2 100644
--- a/libbb/pw_encrypt_des.c
+++ b/libbb/pw_encrypt_des.c
@@ -713,11 +713,15 @@ to64_msb_first(char *s, unsigned v)
 static char *
 NOINLINE
 des_crypt(struct des_ctx *ctx, char output[DES_OUT_BUFSIZE],
-                const unsigned char *key, const unsigned char *setting)
+                const unsigned char *key, const unsigned char *salt_str)
 {
         uint32_t salt, r0, r1, keybuf[2];
         uint8_t *q;
 
+        /* Bad salt? Mimic crypt() API - return NULL */
+        if (!salt_str[0] || !salt_str[1])
+                return NULL;
+
         /*
          * Copy the key, shifting each character up by one bit
          * and padding with zeros.
@@ -732,22 +736,15 @@ des_crypt(struct des_ctx *ctx, char output[DES_OUT_BUFSIZE],
         des_setkey(ctx, (char *)keybuf);
 
         /*
-         * setting - 2 bytes of salt
+         * salt_str - 2 bytes of salt
          * key - up to 8 characters
          */
-        salt = (ascii_to_bin(setting[1]) << 6)
-             |  ascii_to_bin(setting[0]);
-
-        output[0] = setting[0];
-        /*
-         * If the encrypted password that the salt was extracted from
-         * is only 1 character long, the salt will be corrupted.  We
-         * need to ensure that the output string doesn't have an extra
-         * NUL in it!
-         */
-        output[1] = setting[1] ? setting[1] : output[0];
-
+        output[0] = salt_str[0];
+        output[1] = salt_str[1];
+        salt = (ascii_to_bin(salt_str[1]) << 6)
+             |  ascii_to_bin(salt_str[0]);
         setup_salt(ctx, salt);
+
         /* Do it. */
         do_des(ctx, /*0, 0,*/ &r0, &r1, 25 /* count */);