Relevant BUGIDs: 521314

Purpose of commit: bugfix

Commit summary:
---------------
bigcrypt does not match crypt when password length is too long.
This led to a pam_unix problem when the module had not set the
password in bigcrypt mode, but was trying to compare with bigcrypt
output. The fix is to use the stored password as a guide to how much
of the encrypted password to compare against.

1 files changed, 10 insertions, 1 deletions

diff --git a/modules/pam_unix/unix_chkpwd.c b/modules/pam_unix/unix_chkpwd.c
index 9581d046..9ba11041 100644
--- a/modules/pam_unix/unix_chkpwd.c
+++ b/modules/pam_unix/unix_chkpwd.c
@@ -149,7 +149,16 @@ static int _unix_verify_password(const char *name, const char *p, int opt)
 		}
 	} else {
 		pp = bigcrypt(p, salt);
-		if (strcmp(pp, salt) == 0) {
+		/*
+		 * Note, we are comparing the bigcrypt of the password with
+		 * the contents of the password field. If the latter was
+		 * encrypted with regular crypt (and not bigcrypt) it will
+		 * have been truncated for storage relative to the output
+		 * of bigcrypt here. As such we need to compare only the
+		 * stored string with the subset of bigcrypt's result.
+		 * Bug 521314: the strncmp comparison is for legacy support.
+		 */
+		if (strncmp(pp, salt, strlen(salt)) == 0) {
 			retval = UNIX_PASSED;
 		}
 	}