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Cygwin: console: Fix a race issue between close() and open().

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The open() call for console sometimes fails if the console owner
process is closing the console by close() at the same time. This
is due to mismatch state of con.owner variable and attaching state
to the console. With this patch, checking con.owner and attaching
to con.owner sequence in open(), and resetting con.owner and freeing
console sequence in close() are guarded by output_mutex to avoid
such a race issue.
Addresses: https://cygwin.com/pipermail/cygwin/2024-March/255575.html

Fixes: 3721a756b0d8 ("Cygwin: console: Make the console accessible from other terminals.")
Reported-by: Kate Deplaix <kit-ty-kate@outlook.com>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
This commit is contained in:
Takashi Yano 2024-03-04 11:32:34 +09:00
parent abb532a87f
commit b160b690b6
2 changed files with 38 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
winsup/cygwin/fhandler/console.cc
View File

@ -687,14 +687,6 @@ fhandler_console::set_unit ()
{
devset = (fh_devices) shared_console_info[unit]->tty_min_state.getntty ();
_tc = &(shared_console_info[unit]->tty_min_state);
if (!created)
{
while (con.owner > MAX_PID)
Sleep (1);
pinfo p (con.owner);
if (!p)
con.owner = myself->pid;
}
}
dev ().parse (devset);
@ -1744,11 +1736,23 @@ fhandler_console::open (int flags, mode_t)
set_handle (NULL);
set_output_handle (NULL);
setup_io_mutex ();
acquire_output_mutex (mutex_timeout);
do
{
pinfo p (con.owner);
if (!p)
con.owner = myself->pid;
}
while (false);
/* Open the input handle as handle_ */
bool err = false;
DWORD resume_pid = attach_console (con.owner, &err);
if (err)
{
release_output_mutex ();
set_errno (EACCES);
return 0;
}
@ -1759,6 +1763,7 @@ fhandler_console::open (int flags, mode_t)
if (h == INVALID_HANDLE_VALUE)
{
release_output_mutex ();
__seterrno ();
return 0;
}
@ -1768,6 +1773,7 @@ fhandler_console::open (int flags, mode_t)
resume_pid = attach_console (con.owner, &err);
if (err)
{
release_output_mutex ();
set_errno (EACCES);
return 0;
}
@ -1778,14 +1784,16 @@ fhandler_console::open (int flags, mode_t)
if (h == INVALID_HANDLE_VALUE)
{
release_output_mutex ();
__seterrno ();
return 0;
}
set_output_handle (h);
handle_set.output_handle = h;
release_output_mutex ();
wpbuf.init ();
setup_io_mutex ();
handle_set.input_mutex = input_mutex;
handle_set.output_mutex = output_mutex;
@ -1895,25 +1903,20 @@ fhandler_console::close ()
}
}
release_output_mutex ();
if (shared_console_info[unit] && con.owner == myself->pid
&& master_thread_started)
if (shared_console_info[unit] && con.owner == myself->pid)
{
char name[MAX_PATH];
shared_name (name, CONS_THREAD_SYNC, get_minor ());
thread_sync_event = OpenEvent (MAXIMUM_ALLOWED, FALSE, name);
con.owner = MAX_PID + 1;
WaitForSingleObject (thread_sync_event, INFINITE);
CloseHandle (thread_sync_event);
if (master_thread_started)
{
char name[MAX_PATH];
shared_name (name, CONS_THREAD_SYNC, get_minor ());
thread_sync_event = OpenEvent (MAXIMUM_ALLOWED, FALSE, name);
con.owner = MAX_PID + 1;
WaitForSingleObject (thread_sync_event, INFINITE);
CloseHandle (thread_sync_event);
}
con.owner = 0;
}
CloseHandle (input_mutex);
input_mutex = NULL;
CloseHandle (output_mutex);
output_mutex = NULL;
CloseHandle (get_handle ());
CloseHandle (get_output_handle ());
@ -1926,6 +1929,13 @@ fhandler_console::close ()
|| get_device () == (dev_t) myself->ctty))
free_console ();
release_output_mutex ();
CloseHandle (input_mutex);
input_mutex = NULL;
CloseHandle (output_mutex);
output_mutex = NULL;
if (shared_console_info[unit] && myself->ctty != tc ()->ntty)
{
UnmapViewOfFile ((void *) shared_console_info[unit]);

4
winsup/cygwin/release/3.5.2
View File

@ -5,3 +5,7 @@ Fixes:
is already unmapped due to race condition. To avoid this issue,
shared console memory will be kept mapped if it belongs to CTTY.
Addresses: https://cygwin.com/pipermail/cygwin/2024-February/255561.html
- Fix a race issue between console open() and close() which is caused
by state mismatch between con.owner and console attaching state.
Addresses: https://cygwin.com/pipermail/cygwin/2024-March/255575.html