From 7e78e373f53f792cf7295345df7fdf75b9706903 Mon Sep 17 00:00:00 2001
From: Robert Spalek <robert@ucw.cz>
Date: Wed, 23 Jun 2004 16:48:25 +0000
Subject: [PATCH] MJ's idea: - only lock the memory by mprotect() once -
 decompress into the middle of the buffer s.t. the barrier is at the distance 
  as it used before (needs adding one pointer to the structure)

---
 lib/lizard-safe.c | 18 ++++++++++--------
 lib/lizard.h      |  2 +-
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/lib/lizard-safe.c b/lib/lizard-safe.c
index c26a53bc..c615acc4 100644
--- a/lib/lizard-safe.c
+++ b/lib/lizard-safe.c
@@ -22,17 +22,19 @@ struct lizard_buffer *
 lizard_alloc(uns max_len)
 {
   struct lizard_buffer *buf = xmalloc(sizeof(struct lizard_buffer));
-  buf->len = ALIGN(max_len + PAGE_SIZE, PAGE_SIZE);
-  buf->ptr = mmap(NULL, buf->len, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
-  if (buf->ptr == MAP_FAILED)
+  buf->len = ALIGN(max_len, PAGE_SIZE);
+  buf->start = mmap(NULL, buf->len + PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (buf->start == MAP_FAILED)
     die("mmap(anonymous): %m");
+  if (mprotect(buf->start + buf->len, PAGE_SIZE, PROT_NONE) < 0)
+    die("mprotect: %m");
   return buf;
 }
 
 void
 lizard_free(struct lizard_buffer *buf)
 {
-  munmap(buf->ptr, buf->len);
+  munmap(buf->start, buf->len + PAGE_SIZE);
   xfree(buf);
 }
 
@@ -51,27 +53,27 @@ lizard_decompress_safe(byte *in, struct lizard_buffer *buf, uns expected_length)
    * is caught in the case of buffer-overflow.  The function is not re-entrant
    * because of a static longjmp handler.  */
 {
-  volatile uns lock_offset = ALIGN(expected_length, PAGE_SIZE);
-  if (lock_offset + PAGE_SIZE > buf->len)
+  uns lock_offset = ALIGN(expected_length, PAGE_SIZE);
+  if (lock_offset > buf->len)
   {
     errno = EFBIG;
     return -1;
   }
-  mprotect(buf->ptr + lock_offset, PAGE_SIZE, PROT_NONE);
   volatile sighandler_t old_handler = signal(SIGSEGV, sigsegv_handler);
   int len, err;
   if (!setjmp(safe_decompress_jump))
   {
+    buf->ptr = buf->start + buf->len - lock_offset;
     len = lizard_decompress(in, buf->ptr);
     err = errno;
   }
   else
   {
+    buf->ptr = NULL;
     len = -1;
     err = EFAULT;
   }
   signal(SIGSEGV, old_handler);
-  mprotect(buf->ptr + lock_offset, PAGE_SIZE, PROT_READ | PROT_WRITE);
   errno = err;
   return len;
 }
diff --git a/lib/lizard.h b/lib/lizard.h
index 52ddf8b3..e84b5119 100644
--- a/lib/lizard.h
+++ b/lib/lizard.h
@@ -30,7 +30,7 @@ int lizard_decompress(byte *in, byte *out);
 /* lizard-safe.c */
 struct lizard_buffer {
   uns len;
-  void *ptr;
+  void *start, *ptr;
 };
 
 struct lizard_buffer *lizard_alloc(uns max_len);
-- 
2.39.2