The request processing is delayed by a timer. Since nginx updates
internal time once at the start of each event loop iteration, this
normally ensures constant time delay, adding a mitigation from
time-based attacks.
A notable exception to this is the case when there are no additional
events before the timer expires. To ensure constant-time processing
in this case as well, we trigger an additional event loop iteration
by posting a dummy event for the next event loop iteration.
When "aio" or "aio threads" is used while processing the response body of an
in-memory background subrequest, the subrequest could be finalized with an aio
operation still in progress. Upon aio completion either parent request is
woken or the old r->write_event_handler is called again. The latter may result
in request errors. In either case post_subrequest handler is never called with
the full response body, which is typically expected when using in-memory
subrequests.
Currently in nginx background subrequests are created by the upstream module
and the mirror module. The issue does not manifest itself with these
subrequests because they are header-only. But it can manifest itself with
third-party modules which create in-memory background subrequests.
We used to have default error_page overwrite for 495, 496, and 497, so
a configuration like
error_page 495 /error;
will result in error 400, much like without any error_page configured.
The 494 status code was introduced later (in 3848:de59ad6bf557, nginx 0.9.4),
and relevant changes to ngx_http_core_error_page() were missed, resulting
in inconsistent behaviour of "error_page 494" - with error_page configured
it results in 494 being returned instead of 400.
Reported by Frank Liu,
http://mailman.nginx.org/pipermail/nginx/2020-February/058957.html.
In "co64" atom chunk start offset is a 64-bit unsigned integer. When trimming
the "mdat" atom, chunk offsets are casted to off_t values which are typically
64-bit signed integers. A specially crafted mp4 file with huge chunk offsets
may lead to off_t overflow and result in negative trim boundaries.
The consequences of the overflow are:
- Incorrect Content-Length header value in the response.
- Negative left boundary of the response file buffer holding the trimmed "mdat".
This leads to pread()/sendfile() errors followed by closing the client
connection.
On rare systems where off_t is a 32-bit integer, this scenario is also feasible
with the "stco" atom.
The fix is to add checks which make sure data chunks referenced by each track
are within the mp4 file boundaries. Additionally a few more checks are added to
ensure mp4 file consistency and log errors.
Duplicate "Host" headers were allowed in nginx 0.7.0 (revision b9de93d804ea)
as a workaround for some broken Motorola phones which used to generate
requests with two "Host" headers[1]. It is believed that this workaround
is no longer relevant.
[1] http://mailman.nginx.org/pipermail/nginx-ru/2008-May/017845.html
The "identity" transfer coding has been removed in RFC 7230. It is
believed that it is not used in real life, and at the same time it
provides a potential attack vector.
We anyway do not support more than one transfer encoding, so accepting
requests with multiple Transfer-Encoding headers doesn't make sense.
Further, we do not handle multiple headers, and ignore anything but
the first header.
Reported by Filippo Valsorda.
A connection could get stuck without timers if a client has partially sent
the HEADERS frame such that it was split on the individual header boundary.
In this case, it cannot be processed without the rest of the HEADERS frame.
The fix is to call ngx_http_v2_state_headers_save() in this case. Normally,
it would be called from the ngx_http_v2_state_header_block() handler on the
next iteration, when there is not enough data to continue processing. This
isn't the case if recv_buffer became empty and there's no more data to read.
With the recent change to prevent frames flood in d4448892a294,
nginx will finalize the connection with NGX_HTTP_V2_INTERNAL_ERROR
whenever flood is detected, causing nginx aborting or stopping if
the debug_points directive is used in nginx config.
Previous change 1ce3f01a4355 incorrectly introduced processing of the
ngx_posted_next_events queue at the end of operation, effectively making
posted next events a nop, since at the end of an event loop iteration
the queue is always empty. Correct approach is to move events to the
ngx_posted_events queue at an iteration start, as it was done previously.
Further, in some cases the c->read event might be already in the
ngx_posted_events queue, and calling ngx_post_event() with the
ngx_posted_next_events queue won't do anything. To make sure the event
will be correctly placed into the ngx_posted_next_events queue
we now check if it is already posted.
Introduced in 9d2ad2fb4423 available bytes handling in SSL relied
on connection read handler being overwritten to set the ready flag
and the amount of available bytes. This approach is, however, does
not work properly when connection read handler is changed, for example,
when switching to a next pipelined request, and can result in unexpected
connection timeouts, see here:
http://mailman.nginx.org/pipermail/nginx-devel/2019-December/012825.html
Fix is to introduce ngx_event_process_posted_next() instead, which
will set ready and available regardless of how event handler is set.
When ngx_http_v2_close_stream_handler() is used to retry stream close
after queued frames are sent, client timeouts on the stream can be
logged multiple times and/or in addition to already happened errors.
To resolve this, separate ngx_http_v2_retry_close_stream_handler()
was introduced, which does not try to log timeouts.
If a stream is closed with queued frames, it is possible that no further
write events will occur on the stream, leading to the socket leak.
To fix this, the stream's fake connection read handler is set to
ngx_http_v2_close_stream_handler(), to make sure that finalizing the
connection with ngx_http_v2_finalize_connection() will be able to
close the stream regardless of the current number of queued frames.
Additionally, the stream's fake connection fc->error flag is explicitly
set, so ngx_http_v2_handle_stream() will post a write event when queued
frames are finally sent even if stream flow control window is exhausted.
These checks were missed when chunked support was introduced. And also
added an explicit error message to ngx_http_dav_copy_move_handler()
(it was missed for some reason, in contrast to DELETE and MKCOL handlers).
While empty replacements were caught at run-time, parsing code
of the "rewrite" directive expects that a minimum length of the
"replacement" argument is 1.
If a rewritten URI has the null character, only a part of URI was
copied to a memory buffer allocated for path. In some setups this
could be exploited to expose uninitialized memory via the Location
header.
The "alias" directive cannot be used in the same location where URI
was rewritten. This has been detected in the "rewrite ... break"
case, but not when the standalone "break" directive was used.
This change also fixes proxy_pass with URI component in a similar
case:
location /aaa/ {
rewrite ^ /xxx/yyy;
break;
proxy_pass http://localhost:8080/bbb/;
}
Previously, the "/bbb/yyy" would be sent to a backend instead of
"/xxx/yyy". And if location's prefix was longer than the rewritten
URI, a segmentation fault might occur.
Previously, connections returned from keepalive cache had c->data
pointing to the keepalive cache item. While this shouldn't be a problem
for correct code, as c->data is not expected to be used before it is set,
explicitly clearing it might help to avoid confusion.
Previously only an rbtree was associated with a limit_conn. To make it
possible to associate more data with a limit_conn, shared context is introduced
similar to limit_req. Also, shared pool pointer is kept in a way similar to
limit_req.
Maxim Dounin
Ruslan Ermilov
Roman Arutyunyan
Dmitry Volyntsev
Sergey Kandaurov
Vladimir Homutov
Daniil Bondarev
Sergey A. Osokin