commit 7c6a6149a91d2e240a5a63f981c5d07d681df725
Author: Willy Tarreau <w@1wt.eu>
Date:   Mon Jan 14 17:07:39 2019 +0100

    BUG/MINOR: backend: BE_LB_LKUP_CHTREE is a value, not a bit
    
    There are a few instances where the lookup algo is tested against
    BE_LB_LKUP_CHTREE using a binary "AND" operation while this macro
    is a value among a set, and not a bit. The test happens to work
    because the value is exactly 4 and no bit overlaps with the other
    possible values but this is a latent bug waiting for a new LB algo
    to appear to strike. At the moment the only other algo sharing a bit
    with it is the "first" algo which is never supported in the same code
    places.
    
    This fix should be backported to maintained versions for safety if it
    passes easily, otherwise it's not important as it will not fix any
    visible issue.
    
    (cherry picked from commit 6c30be52da3d949a8dd6fb5e2de7319c031e656e)
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    (cherry picked from commit 48147c424680b7e887fb176662d58d87baa16098)
    Signed-off-by: William Lallemand <wlallemand@haproxy.org>

diff --git a/src/backend.c b/src/backend.c
index 4c4044a6..0cf14cfd 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -183,7 +183,7 @@ static struct server *get_server_sh(struct proxy *px, const char *addr, int len,
 	if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
 		h = full_hash(h);
  hash_done:
-	if (px->lbprm.algo & BE_LB_LKUP_CHTREE)
+	if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 		return chash_get_server_hash(px, h, avoid);
 	else
 		return map_get_server_hash(px, h);
@@ -236,7 +236,7 @@ static struct server *get_server_uh(struct proxy *px, char *uri, int uri_len, co
 	if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
 		hash = full_hash(hash);
  hash_done:
-	if (px->lbprm.algo & BE_LB_LKUP_CHTREE)
+	if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 		return chash_get_server_hash(px, hash, avoid);
 	else
 		return map_get_server_hash(px, hash);
@@ -293,7 +293,7 @@ static struct server *get_server_ph(struct proxy *px, const char *uri, int uri_l
 				if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
 					hash = full_hash(hash);
 
-				if (px->lbprm.algo & BE_LB_LKUP_CHTREE)
+				if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 					return chash_get_server_hash(px, hash, avoid);
 				else
 					return map_get_server_hash(px, hash);
@@ -367,7 +367,7 @@ static struct server *get_server_ph_post(struct stream *s, const struct server *
 				if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
 					hash = full_hash(hash);
 
-				if (px->lbprm.algo & BE_LB_LKUP_CHTREE)
+				if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 					return chash_get_server_hash(px, hash, avoid);
 				else
 					return map_get_server_hash(px, hash);
@@ -463,7 +463,7 @@ static struct server *get_server_hh(struct stream *s, const struct server *avoid
 	if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
 		hash = full_hash(hash);
  hash_done:
-	if (px->lbprm.algo & BE_LB_LKUP_CHTREE)
+	if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 		return chash_get_server_hash(px, hash, avoid);
 	else
 		return map_get_server_hash(px, hash);
@@ -507,7 +507,7 @@ static struct server *get_server_rch(struct stream *s, const struct server *avoi
 	if ((px->lbprm.algo & BE_LB_HASH_MOD) == BE_LB_HMOD_AVAL)
 		hash = full_hash(hash);
  hash_done:
-	if (px->lbprm.algo & BE_LB_LKUP_CHTREE)
+	if ((px->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 		return chash_get_server_hash(px, hash, avoid);
 	else
 		return map_get_server_hash(px, hash);
@@ -615,7 +615,7 @@ int assign_server(struct stream *s)
 		case BE_LB_LKUP_CHTREE:
 		case BE_LB_LKUP_MAP:
 			if ((s->be->lbprm.algo & BE_LB_KIND) == BE_LB_KIND_RR) {
-				if (s->be->lbprm.algo & BE_LB_LKUP_CHTREE)
+				if ((s->be->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 					srv = chash_get_next_server(s->be, prev_srv);
 				else
 					srv = map_get_server_rr(s->be, prev_srv);
@@ -691,7 +691,7 @@ int assign_server(struct stream *s)
 			 * back to round robin on the map.
 			 */
 			if (!srv) {
-				if (s->be->lbprm.algo & BE_LB_LKUP_CHTREE)
+				if ((s->be->lbprm.algo & BE_LB_LKUP) == BE_LB_LKUP_CHTREE)
 					srv = chash_get_next_server(s->be, prev_srv);
 				else
 					srv = map_get_server_rr(s->be, prev_srv);