- lizard_alloc() turns on the wrapper for SIGSEGV and lizard_free() restores

[libucw.git] / lib / lizard-safe.c

diff --git a/lib/lizard-safe.c b/lib/lizard-safe.c
index fb45f8bf17f8a6d83b694485f8ed10dc80f009fd..6d0b10c952b585e0cd93cf9bd24583f53fd9fb67 100644 (file)
--- a/lib/lizard-safe.c
+++ b/lib/lizard-safe.c
@@ -21,28 +21,28 @@
 struct lizard_buffer *
 lizard_alloc(uns max_len)
 {
-  static byte *zero = "/dev/zero";
-  int fd = open(zero, O_RDWR);
-  if (fd < 0)
-    die("open(%s): %m", zero);
   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_PRIVATE, fd, 0);
-  if (buf->ptr == MAP_FAILED)
-    die("mmap(%s): %m", zero);
+  buf->len = ALIGN(max_len + 3, PAGE_SIZE);            // +3 due to the unaligned access
+  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");
+  buf->old_sigsegv_handler = handle_signal(SIGSEGV);
   return buf;
 }
 
 void
 lizard_free(struct lizard_buffer *buf)
 {
-  munmap(buf->ptr, buf->len);
+  munmap(buf->start, buf->len + PAGE_SIZE);
+  signal(SIGSEGV, buf->old_sigsegv_handler);
   xfree(buf);
 }
 
 static jmp_buf safe_decompress_jump;
 static void
-sigsegv_handler(int UNUSED whatsit)
+sigsegv_handler(void)
 {
   log(L_ERROR, "SIGSEGV caught in lizard_decompress()");
   longjmp(safe_decompress_jump, 1);
@@ -55,27 +55,28 @@ 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.  */
 {
-  uns lock_offset = ALIGN(expected_length, PAGE_SIZE);
-  if (lock_offset + PAGE_SIZE > buf->len)
+  uns lock_offset = ALIGN(expected_length + 3, PAGE_SIZE);     // +3 due to the unaligned access
+  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);
+  volatile my_sighandler_t old_handler = signal_handler[SIGSEGV];
+  signal_handler[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);
+  signal_handler[SIGSEGV] = old_handler;
   errno = err;
   return len;
 }