login: fix pos-array allocation

GREEDY_REALLOC takes a pointer to the real size, not the array-width as
argument. Therefore, our array is currently way to small to keep the seat
positions.

Introduce GREEDY_REALLOC0_T() as typed version of GREEDY_REALLOC and store
the array-width instead of array-size.

2 files changed, 10 insertions, 1 deletions

diff --git a/src/login/logind-seat.c b/src/login/logind-seat.c
index 631be5f740..36ec7ed757 100644
--- a/src/login/logind-seat.c
+++ b/src/login/logind-seat.c
@@ -475,7 +475,7 @@ void seat_claim_position(Seat *s, Session *session, unsigned int pos) {
         if (seat_has_vts(s))
                 pos = session->vtnr;
 
-        if (!GREEDY_REALLOC0(s->positions, s->position_count, pos + 1))
+        if (!GREEDY_REALLOC0_T(s->positions, s->position_count, pos + 1))
                 return;
 
         seat_evict_position(s, session);
diff --git a/src/shared/util.h b/src/shared/util.h
index 9913fcefae..78b1444739 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -723,6 +723,15 @@ void* greedy_realloc0(void **p, size_t *allocated, size_t need);
 #define GREEDY_REALLOC0(array, allocated, need) \
         greedy_realloc0((void**) &(array), &(allocated), sizeof((array)[0]) * (need))
 
+#define GREEDY_REALLOC0_T(array, count, need)                           \
+        ({                                                              \
+                size_t _size = (count) * sizeof((array)[0]);            \
+                void *_ptr = GREEDY_REALLOC0((array), _size, (need));   \
+                if (_ptr)                                               \
+                        (count) = _size / sizeof((array)[0]);           \
+                _ptr;                                                   \
+        })
+
 static inline void _reset_errno_(int *saved_errno) {
         errno = *saved_errno;
 }