fix: crash during SORT DESC call (#3637)

fixes #3636

The problem was that instead of implementing GT operator, we implemented
!LT, which is GE operator. As a result the iterators inside the sort algorithm reached
out of bounds.

---------

Signed-off-by: Roman Gershman <[email protected]>

Author: romange

src/server/generic_family.cc

@@ -1184,9 +1184,10 @@ void GenericFamily::Sort(CmdArgList args, ConnectionContext* cntx) {
                         });
     } else {
       std::sort(entries.begin(), entries.end(),
-                [reversed, &entries](const auto& lhs, const auto& rhs) {
-                  DCHECK(&rhs < &(*entries.end()) && &rhs >= &(*entries.begin()));
-                  return bool(lhs.Cmp() < rhs.Cmp()) ^ reversed;
+                [reversed, &entries](const auto& lhs, const auto& rhs) -> bool {
+                  DCHECK((&rhs - entries.data()) >= 0);
+                  DCHECK((&rhs - entries.data()) < int64_t(entries.size()));
+                  return reversed ? rhs.Cmp() < lhs.Cmp() : lhs.Cmp() < rhs.Cmp();
                 });
     }
 

src/server/generic_family_test.cc

@@ -481,6 +481,15 @@ TEST_F(GenericFamilyTest, Sort) {
   ;
 }
 
+TEST_F(GenericFamilyTest, SortBug3636) {
+  Run({"RPUSH", "foo", "1.100000023841858", "1.100000023841858", "1.100000023841858", "-15710",
+       "1.100000023841858", "1.100000023841858", "1.100000023841858", "-15710", "-15710",
+       "1.100000023841858", "-15710", "-15710", "-15710", "-15710", "1.100000023841858", "-15710",
+       "-15710"});
+  auto resp = Run({"SORT", "foo", "desc", "alpha"});
+  ASSERT_THAT(resp, ArrLen(17));
+}
+
 TEST_F(GenericFamilyTest, TimeNoKeys) {
   auto resp = Run({"time"});
   EXPECT_THAT(resp, ArrLen(2));