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From: Maxim Dounin <mdounin@mdounin.ru>
Date: Tue, 31 May 2016 05:13:30 +0300
Subject: 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.
Backported by 1.11.1 for debian.
---
src/os/unix/ngx_files.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/src/os/unix/ngx_files.c b/src/os/unix/ngx_files.c
index c3ae47f..1970184 100644
--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -183,6 +183,12 @@ ngx_write_chain_to_file(ngx_file_t *file, ngx_chain_t *cl, off_t offset,
/* create the iovec and coalesce the neighbouring bufs */
while (cl && vec.nelts < IOV_MAX) {
+
+ if (ngx_buf_special(cl->buf)) {
+ cl = cl->next;
+ continue;
+ }
+
if (prev == cl->buf->pos) {
iov->iov_len += cl->buf->last - cl->buf->pos;
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