From 8c4cadec6d436b98902920d034afa4237455138c Mon Sep 17 00:00:00 2001
From: Mikolaj Zalewski <mikolaj@zalewski.pl>
Date: Thu, 11 Oct 2007 13:14:46 -0700
Subject: [PATCH] server: make the pids/tids more random
---
 server/main.c    |    9 +++++++++
 server/process.c |   48 +++++++++++++++++++++++++++++++-----------------
 2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/server/main.c b/server/main.c
index c839c18..ab2a4a4 100644
--- a/server/main.c
+++ b/server/main.c
@@ -115,6 +115,14 @@ static void sigterm_handler( int signum 
     exit(1);  /* make sure atexit functions get called */
 }
 
+static void init_random()
+{
+    time_t t;
+
+    time(&t);
+    srandom(t);
+}
+
 int main( int argc, char *argv[] )
 {
     parse_args( argc, argv );
@@ -132,6 +140,7 @@ int main( int argc, char *argv[] )
     setvbuf( stderr, NULL, _IOLBF, 0 );
 
     if (debug_level) fprintf( stderr, "wineserver: starting (pid=%ld)\n", (long) getpid() );
+    init_random();
     init_signals();
     init_directories();
     init_registry();
diff --git a/server/process.c b/server/process.c
index 8ca20d8..3f44908 100644
--- a/server/process.c
+++ b/server/process.c
@@ -139,33 +139,44 @@ struct ptid_entry
 };
 
 static struct ptid_entry *ptid_entries;     /* array of ptid entries */
-static unsigned int used_ptid_entries;      /* number of entries in use */
 static unsigned int alloc_ptid_entries;     /* number of allocated entries */
 static unsigned int next_free_ptid;         /* next free entry */
 static unsigned int last_free_ptid;         /* last free entry */
 
 #define PTID_OFFSET 8  /* offset for first ptid value */
 
+/* some apps uses the pid/tid as random seed. This adds a bit of randomness to them.
+ * count must be a power of 2 */
+static void randomize_and_add_ptids( int base, int count )
+{
+    int step, first, last;
+    int i;
+
+    step = random() % (count/2);
+    step = 2*step + 1;
+
+    for (i = 0; i < count; i++)
+    {
+        ptid_entries[base + i].next = base + ((i + step) % count) + PTID_OFFSET;
+        ptid_entries[base + i].ptr = NULL;
+    }
+
+    last = base + (random() % count);
+    first = ptid_entries[last].next - PTID_OFFSET;
+    ptid_entries[last].next = 0;
+    last_free_ptid = last + PTID_OFFSET;
+    next_free_ptid = first + PTID_OFFSET;
+}
+
 /* allocate a new process or thread id */
 unsigned int alloc_ptid( void *ptr )
 {
     struct ptid_entry *entry;
     unsigned int id;
 
-    if (used_ptid_entries < alloc_ptid_entries)
-    {
-        id = used_ptid_entries + PTID_OFFSET;
-        entry = &ptid_entries[used_ptid_entries++];
-    }
-    else if (next_free_ptid)
+    if (!next_free_ptid)  /* need to grow the array */
     {
-        id = next_free_ptid;
-        entry = &ptid_entries[id - PTID_OFFSET];
-        if (!(next_free_ptid = entry->next)) last_free_ptid = 0;
-    }
-    else  /* need to grow the array */
-    {
-        unsigned int count = alloc_ptid_entries + (alloc_ptid_entries / 2);
+        unsigned int count = 2*alloc_ptid_entries;
         if (!count) count = 64;
         if (!(entry = realloc( ptid_entries, count * sizeof(*entry) )))
         {
@@ -173,11 +184,14 @@ unsigned int alloc_ptid( void *ptr )
             return 0;
         }
         ptid_entries = entry;
+        randomize_and_add_ptids(alloc_ptid_entries, count - alloc_ptid_entries);
         alloc_ptid_entries = count;
-        id = used_ptid_entries + PTID_OFFSET;
-        entry = &ptid_entries[used_ptid_entries++];
     }
 
+    id = next_free_ptid;
+    entry = &ptid_entries[id - PTID_OFFSET];
+    if (!(next_free_ptid = entry->next)) last_free_ptid = 0;
+
     entry->ptr = ptr;
     return id;
 }
@@ -201,7 +215,7 @@ void free_ptid( unsigned int id )
 void *get_ptid_entry( unsigned int id )
 {
     if (id < PTID_OFFSET) return NULL;
-    if (id - PTID_OFFSET >= used_ptid_entries) return NULL;
+    if (id - PTID_OFFSET >= alloc_ptid_entries) return NULL;
     return ptid_entries[id - PTID_OFFSET].ptr;
 }
 
-- 
1.4.1