From 94c9baeb229d8d41d28bff1ec5062477158ae83b Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Tue, 1 Jan 2019 14:45:27 -0500
Subject: [PATCH] temporary workaround for Pixel 3 camera UAF

---
 h_malloc.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/h_malloc.c b/h_malloc.c
index 8d76aad..fda893b 100644
--- a/h_malloc.c
+++ b/h_malloc.c
@@ -74,6 +74,8 @@ static union {
         int metadata_pkey;
         bool pkey_state_preserved_on_fork;
 #endif
+        bool zero_on_free;
+        bool purge_slabs;
     };
     char padding[PAGE_SIZE];
 } ro __attribute__((aligned(PAGE_SIZE)));
@@ -426,7 +428,7 @@ static void *slot_pointer(size_t size, void *slab, size_t slot) {
 }
 
 static void write_after_free_check(const char *p, size_t size) {
-    if (!WRITE_AFTER_FREE_CHECK) {
+    if (!WRITE_AFTER_FREE_CHECK || !ro.zero_on_free) {
         return;
     }
 
@@ -668,7 +670,7 @@ static inline void deallocate_small(void *p, const size_t *expected_size) {
             }
         }
 
-        if (ZERO_ON_FREE) {
+        if (ro.zero_on_free) {
             memset(p, 0, size - canary_size);
         }
     }
@@ -745,7 +747,7 @@ static inline void deallocate_small(void *p, const size_t *expected_size) {
         metadata->prev = NULL;
 
         if (c->empty_slabs_total + slab_size > max_empty_slabs_total) {
-            if (!memory_map_fixed(slab, slab_size)) {
+            if (ro.purge_slabs && !memory_map_fixed(slab, slab_size)) {
                 label_slab(slab, slab_size, class);
                 stats_slab_deallocate(c, slab_size);
                 enqueue_free_slab(c, metadata);
@@ -1046,6 +1048,18 @@ static inline void enforce_init(void) {
     }
 }
 
+COLD static void handle_camera_bug(void) {
+    const char expected[] = "/vendor/bin/hw/android.hardware.camera.provider@2.4-service_64";
+    char path[sizeof(expected)];
+    if (readlink("/proc/self/exe", path, sizeof(path)) == -1) {
+        return;
+    }
+    if (strcmp(expected, path) == 0) {
+        ro.zero_on_free = false;
+        ro.purge_slabs = false;
+    }
+}
+
 COLD static void init_slow_path(void) {
     static struct mutex lock = MUTEX_INITIALIZER;
 
@@ -1069,6 +1083,10 @@ COLD static void init_slow_path(void) {
     }
 #endif
 
+    ro.purge_slabs = true;
+    ro.zero_on_free = ZERO_ON_FREE;
+    handle_camera_bug();
+
     if (sysconf(_SC_PAGESIZE) != PAGE_SIZE) {
         fatal_error("page size mismatch");
     }
@@ -1340,7 +1358,7 @@ EXPORT void *h_calloc(size_t nmemb, size_t size) {
     total_size = adjust_size_for_canaries(total_size);
     void *p = allocate(arena, total_size);
     thread_seal_metadata();
-    if (!ZERO_ON_FREE && likely(p != NULL) && total_size && total_size <= max_slab_size_class) {
+    if (!ro.zero_on_free && likely(p != NULL) && total_size && total_size <= max_slab_size_class) {
         memset(p, 0, total_size - canary_size);
     }
     return p;