Audit of caml_read_fd: update offset and max pointer

gadmm · gadmm · commit 8971cec1ba4e · 2020-07-12T17:48:18.000+02:00
Only stdin is global in Stdlib, and it is not seekable, so its state
remained valid on exception. However it does not cost much to keep the
offset and the max pointer up to date in all situtations when an
interrupt arises.

In addition, one can be suspicious that channel locks may leak, which
can cause deadlocks. However, this is already dealt with Unlock_exn.
diff --git a/runtime/io.c b/runtime/io.c
@@ -301,7 +301,25 @@ CAMLexport int caml_read_fd(int fd, int flags, void * buf, int n)
   return retcode;
 }
 
-/* caml_do_read is exported for Cash */
+// raises
+static int read_fd_into_channel(struct channel * channel, char * buf)
+{
+  int n;
+  value exn = Val_unit;
+  n = caml_read_fd_exn(channel->fd, channel->flags, buf,
+                       channel->end - buf, &exn);
+  if (n <= 0) {
+    caml_raise_if_exception(exn);
+    CAMLassert(n == 0);
+    return n;
+  }
+  channel->offset += n;
+  channel->max = buf + n;
+  caml_raise_if_exception(exn);
+  return n;
+}
+
+/* caml_do_read is exported for Cash. Raises. */
 CAMLexport int caml_do_read(int fd, char *p, unsigned int n)
 {
   return caml_read_fd(fd, 0, p, n);
@@ -310,12 +328,8 @@ CAMLexport int caml_do_read(int fd, char *p, unsigned int n)
 CAMLexport unsigned char caml_refill(struct channel *channel)
 {
   int n;
-
-  n = caml_read_fd(channel->fd, channel->flags,
-                   channel->buff, channel->end - channel->buff);
+  n = read_fd_into_channel(channel, channel->buff);
   if (n == 0) caml_raise_end_of_file();
-  channel->offset += n;
-  channel->max = channel->buff + n;
   channel->curr = channel->buff + 1;
   return (unsigned char)(channel->buff[0]);
 }
@@ -349,10 +363,7 @@ CAMLexport int caml_getblock(struct channel *channel, char *p, intnat len)
     channel->curr += avail;
     return avail;
   } else {
-    nread = caml_read_fd(channel->fd, channel->flags, channel->buff,
-                         channel->end - channel->buff);
-    channel->offset += nread;
-    channel->max = channel->buff + nread;
+    nread = read_fd_into_channel(channel, channel->buff);
     if (n > nread) n = nread;
     memmove(p, channel->buff, n);
     channel->curr = channel->buff + n;
@@ -421,16 +432,13 @@ CAMLexport intnat caml_input_scan_line(struct channel *channel)
         return -(channel->max - channel->curr);
       }
       /* Fill the buffer as much as possible */
-      n = caml_read_fd(channel->fd, channel->flags,
-                       channel->max, channel->end - channel->max);
+      n = read_fd_into_channel(channel, channel->max);
       if (n == 0) {
         /* End-of-file encountered. Return the number of characters in the
            buffer, with negative sign since we haven't encountered
            a newline. */
         return -(channel->max - channel->curr);
       }
-      channel->offset += n;
-      channel->max += n;
     }
   } while (*p++ != '\n');
   /* Found a newline. Return the length of the line, newline included. */
