patchsets/skey/1.1.5/16_all_skeylogin-len-check.patch


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From OpenBSD.

Author: millert <millert@openbsd.org>
Date:   Wed, 15 Mar 2023 17:01:35 +0000

    Fix the length check when computing a fake challenge for users not in
    the S/Key database. If the system hostname is longer than 126 characters
    this could result in NUL bytes being written past the end of a stack
    buffer. There is no impact on systems with a hostname 126 characters or
    less. Found by Qualys. OK deraadt@

--- skey-1.1.5/skeylogin.c
+++ skey-1.1.5/skeylogin.c
@@ -486,8 +486,8 @@
 			for (p = pbuf; *p && isalnum((u_char)*p); p++)
 				if (isalpha((u_char)*p) && isupper((u_char)*p))
 					*p = tolower((u_char)*p);
-		if (*p && pbuf - p < 4)
-			strncpy(p, "asjd", 4 - (pbuf - p));
+		if (*p && p - pbuf < 4)
+			strncpy(p, "asjd", 4 - (p - pbuf));
 		pbuf[4] = '\0';
 
 		/* Hash the username if possible */