From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 7868) id 7478A385772D; Fri, 4 Aug 2023 08:57:58 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 7478A385772D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1691139478; bh=3jrr1HPzc3fTNf1v6zTkZuVPPtagJk4DTdRKz/s1YwA=; h=From:To:Subject:Date:From; b=Xqs+YrSZtKiV4NxRRe+S9+502YRUogiNaz4JSbNwDgLkW3Smoy/5tGMQl0+IYSFNd M1AApqeafQJFfYqUuL9pHb2G+L/Pi6LbigD9Hg50ZxZzX05JVkc+sGDsAAO2NvyN6j HqjXf993YYQBHixE1CnMKseQoeLI+Eqa1JZra464= Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable From: Takashi Yano To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin] Cygwin: pty: Fix thread safety of readahead buffer handling in pty master. X-Act-Checkin: newlib-cygwin X-Git-Author: Takashi Yano X-Git-Refname: refs/heads/master X-Git-Oldrev: ab78bd2d228027d0ac5a84bfc409444d3ce18948 X-Git-Newrev: 3b4f6217c371cf70d5ec5137436cfa5892bb45e8 Message-Id: <20230804085758.7478A385772D@sourceware.org> Date: Fri, 4 Aug 2023 08:57:58 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=3Dnewlib-cygwin.git;h=3D3b4f6217c37= 1cf70d5ec5137436cfa5892bb45e8 commit 3b4f6217c371cf70d5ec5137436cfa5892bb45e8 Author: Takashi Yano Date: Fri Aug 4 17:45:34 2023 +0900 Cygwin: pty: Fix thread safety of readahead buffer handling in pty mast= er. =20 Previously, though readahead buffer handling in pty master was not fully thread-safe, accept_input() was called from peek_pipe() thread in select.cc. This caused the problem reported in: https://cygwin.com/pipermail/cygwin/2023-July/253984.html =20 The mechanism of the problem is: 1) accept_input() which is called from peek_pipe() thread calls eat_readahead(-1) before reading readahead buffer. This allows writing to the readahead buffer from another (main) thread. 2) The main thread calls fhandler_pty_master::write() just after eat_readahead(-1) was called and before reading the readahead buffer by accept_input() called from peek_pipe() thread. This overwrites the readahead buffer. 3) The read result from readahead buffer which was overwritten is sent to the slave. =20 This patch makes readahead buffer handling fully thread-safe using input_mutex to resolve this issue. =20 Fixes: 7b03b0d8cee0 ("select.cc (peek_pipe): Call flush_to_slave whenev= er we're checking for a pty master.") Reported-by: Thomas Wolff Signed-off-by: Takashi Yano Diff: --- winsup/cygwin/fhandler/pty.cc | 10 +++++----- winsup/cygwin/local_includes/fhandler.h | 8 ++++++++ 2 files changed, 13 insertions(+), 5 deletions(-) diff --git a/winsup/cygwin/fhandler/pty.cc b/winsup/cygwin/fhandler/pty.cc index 8b8c42bc1..db3b77ecf 100644 --- a/winsup/cygwin/fhandler/pty.cc +++ b/winsup/cygwin/fhandler/pty.cc @@ -436,8 +436,10 @@ static int osi; void fhandler_pty_master::flush_to_slave () { + WaitForSingleObject (input_mutex, mutex_timeout); if (get_readahead_valid () && !(get_ttyp ()->ti.c_lflag & ICANON)) accept_input (); + ReleaseMutex (input_mutex); } =20 void @@ -523,8 +525,6 @@ fhandler_pty_master::accept_input () DWORD bytes_left; int ret =3D 1; =20 - WaitForSingleObject (input_mutex, mutex_timeout); - char *p =3D rabuf () + raixget (); bytes_left =3D eat_readahead (-1); =20 @@ -625,7 +625,6 @@ fhandler_pty_master::accept_input () if (write_to =3D=3D get_output_handle ()) SetEvent (input_available_event); /* Set input_available_event only wh= en the data is written to cyg pipe. */ - ReleaseMutex (input_mutex); return ret; } =20 @@ -2235,9 +2234,9 @@ fhandler_pty_master::write (const void *ptr, size_t l= en) { /* This accept_input() call is needed in order to transfer input which is not accepted yet to non-cygwin pipe. */ + WaitForSingleObject (input_mutex, mutex_timeout); if (get_readahead_valid ()) accept_input (); - WaitForSingleObject (input_mutex, mutex_timeout); acquire_attach_mutex (mutex_timeout); fhandler_pty_slave::transfer_input (tty::to_nat, from_master, get_ttyp (), @@ -2305,9 +2304,10 @@ fhandler_pty_master::write (const void *ptr, size_t = len) get_ttyp (), input_available_event); release_attach_mutex (); } - ReleaseMutex (input_mutex); =20 line_edit_status status =3D line_edit (p, len, ti, &ret); + ReleaseMutex (input_mutex); + if (status > line_edit_signalled && status !=3D line_edit_pipe_full) ret =3D -1; return ret; diff --git a/winsup/cygwin/local_includes/fhandler.h b/winsup/cygwin/local_= includes/fhandler.h index 661fe23dc..03b51a7e4 100644 --- a/winsup/cygwin/local_includes/fhandler.h +++ b/winsup/cygwin/local_includes/fhandler.h @@ -2572,6 +2572,14 @@ public: int tcgetpgrp (); void flush_to_slave (); void discard_input (); + void acquire_input_mutex_if_necessary (DWORD ms) + { + WaitForSingleObject (input_mutex, ms); + } + void release_input_mutex_if_necessary (void) + { + ReleaseMutex (input_mutex); + } =20 fhandler_pty_master (void *) {}