[nginx] Range filter: protect from total size overflows.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/1adc6b0d5eaa
branches:  stable-1.12
changeset: 7060:1adc6b0d5eaa
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Tue Jul 11 16:06:23 2017 +0300
description:
Range filter: protect from total size overflows.

The overflow can be used to circumvent the restriction on total size of
ranges introduced in c2a91088b0c0 (1.1.2).  Additionally, overflow
allows producing ranges with negative start (such ranges can be created
by using a suffix, "bytes=-100"; normally this results in 200 due to
the total size check).  These can result in the following errors in logs:

[crit] ... pread() ... failed (22: Invalid argument)
[alert] ... sendfile() failed (22: Invalid argument)

When using cache, it can be also used to reveal cache file header.
It is believed that there are no other negative effects, at least with
standard nginx modules.

In theory, this can also result in memory disclosure and/or segmentation
faults if multiple ranges are allowed, and the response is returned in a
single in-memory buffer.  This never happens with standard nginx modules
though, as well as known 3rd party modules.

Fix is to properly protect from possible overflow when incrementing size.

diffstat:

 src/http/modules/ngx_http_range_filter_module.c |  4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diffs (14 lines):

diff --git a/src/http/modules/ngx_http_range_filter_module.c b/src/http/modules/ngx_http_range_filter_module.c
--- a/src/http/modules/ngx_http_range_filter_module.c
+++ b/src/http/modules/ngx_http_range_filter_module.c
@@ -377,6 +377,10 @@ ngx_http_range_parse(ngx_http_request_t 
             range->start = start;
             range->end = end;
 
+            if (size > NGX_MAX_OFF_T_VALUE - (end - start)) {
+                return NGX_HTTP_RANGE_NOT_SATISFIABLE;
+            }
+
             size += end - start;
 
             if (ranges-- == 0) {