commit a873c161d251abd025008034c0ddef8cd7f39511
Author: Willy Tarreau <w@1wt.eu>
Date:   Mon Oct 29 18:02:54 2018 +0100

    BUG/MEDIUM: auth/threads: use of crypt() is not thread-safe
    
    It was reported here that authentication may fail when threads are
    enabled :
    
        https://bugzilla.redhat.com/show_bug.cgi?id=1643941
    
    While I couldn't reproduce the issue, it's obvious that there is a
    problem with the use of the non-reentrant crypt() function there.
    On Linux systems there's crypt_r() but not on the vast majority of
    other ones. Thus a first approach consists in placing a lock around
    this crypt() call. Another patch may relax it when crypt_r() is
    available.
    
    This fix must be backported to 1.8. Thanks to Ryan O'Hara for the
    quick notification.
    
    (cherry picked from commit 34d4b525a129baa6f52a930ae629ddb1ba4255c2)
    Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 44bd66d1..24fb1d1a 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -373,6 +373,7 @@ enum lock_label {
 	START_LOCK,
 	TLSKEYS_REF_LOCK,
 	PENDCONN_LOCK,
+	AUTH_LOCK,
 	LOCK_LABELS
 };
 struct lock_stat {
@@ -495,6 +496,7 @@ static inline const char *lock_label(enum lock_label label)
 	case START_LOCK:           return "START";
 	case TLSKEYS_REF_LOCK:     return "TLSKEYS_REF";
 	case PENDCONN_LOCK:        return "PENDCONN";
+	case AUTH_LOCK:            return "AUTH";
 	case LOCK_LABELS:          break; /* keep compiler happy */
 	};
 	/* only way to come here is consecutive to an internal bug */
diff --git a/src/auth.c b/src/auth.c
index a2c689f7..e0fb1352 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -28,6 +28,7 @@
 #include <types/global.h>
 #include <common/config.h>
 #include <common/errors.h>
+#include <common/hathreads.h>
 
 #include <proto/acl.h>
 #include <proto/log.h>
@@ -37,6 +38,10 @@
 
 struct userlist *userlist = NULL;    /* list of all existing userlists */
 
+#ifdef CONFIG_HAP_CRYPT
+__decl_hathreads(static HA_SPINLOCK_T auth_lock);
+#endif
+
 /* find targets for selected gropus. The function returns pointer to
  * the userlist struct ot NULL if name is NULL/empty or unresolvable.
  */
@@ -245,7 +250,9 @@ check_user(struct userlist *ul, const char *user, const char *pass)
 
 	if (!(u->flags & AU_O_INSECURE)) {
 #ifdef CONFIG_HAP_CRYPT
+		HA_SPIN_LOCK(AUTH_LOCK, &auth_lock);
 		ep = crypt(pass, u->pass);
+		HA_SPIN_UNLOCK(AUTH_LOCK, &auth_lock);
 #else
 		return 0;
 #endif