Core: skip special buffers on writing (ticket #981).
A special last buffer with cl->buf->pos set to NULL can be present in
a chain when writing request body if chunked encoding was used. This
resulted in a NULL pointer dereference if it happened to be the only
buffer left after a do...while loop iteration in ngx_write_chain_to_file().
The problem originally appeared in nginx 1.3.9 with chunked encoding
support. Additionally, rev. 3832b608dc8d (nginx 1.9.13) changed the
minimum number of buffers to trigger this from IOV_MAX (typically 1024)
to NGX_IOVS_PREALLOCATE (typically 64).
Fix is to skip such buffers in ngx_chain_to_iovec(), much like it is
done in other places.
diff --git a/src/os/unix/ngx_files.c b/src/os/unix/ngx_files.c
index 65c79a2..7fbb7c9 100644
--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -356,6 +356,11 @@
n = 0;
for ( /* void */ ; cl; cl = cl->next) {
+
+ if (ngx_buf_special(cl->buf)) {
+ continue;
+ }
+
size = cl->buf->last - cl->buf->pos;
if (prev == cl->buf->pos) {
