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pt_chown: Clear any signal mask inherited from the parent process.

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If grantpt() is called from a thread that is masking signals (for
instance, from a program using signalfd or using a dedicated
signal-handling thread), then that mask will get inherited to pt_chown.
This means that signals like SIGINT will not interrup pt_chown, so if it
hangs (e.g., because getgrnam("tty") hangs on a remote name service),
Ctrl-C will terminate the parent process but leave pt_chown around. Since
it's setuid, it's hard to kill any other way.

It is safe for pt_chown to unmask all signals, because grantpt() can be
(and usually is) called from an unprivileged process with all signals
unmasked.
This commit is contained in:
Geoffrey Thomas
2015-10-19 19:33:28 +05:30
committed by Siddhesh Poyarekar
parent 361468f226
commit 2028f49dab
2 changed files with 11 additions and 0 deletions
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5
ChangeLog
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@@ -1,3 +1,8 @@
2015-10-19 Geoffrey Thomas <geofft@ldpreload.com>
* login/programs/pt_chown.c: Include signal.h
(main): Clear any signal mask from the parent process.
2015-10-19 Joseph Myers <joseph@codesourcery.com> 2015-10-19 Joseph Myers <joseph@codesourcery.com>
* configure.ac (libc_cv_gnu89_inline): Remove configure test. * configure.ac (libc_cv_gnu89_inline): Remove configure test.

6
login/programs/pt_chown.c
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@@ -23,6 +23,7 @@
#include <grp.h> #include <grp.h>
#include <libintl.h> #include <libintl.h>
#include <locale.h> #include <locale.h>
#include <signal.h>
#include <stdio.h> #include <stdio.h>
#include <stdlib.h> #include <stdlib.h>
#include <string.h> #include <string.h>
@@ -148,6 +149,11 @@ main (int argc, char *argv[])
uid_t euid = geteuid (); uid_t euid = geteuid ();
uid_t uid = getuid (); uid_t uid = getuid ();
int remaining; int remaining;
sigset_t signalset;
/* Clear any signal mask from the parent process. */
sigemptyset (&signalset);
sigprocmask (SIG_SETMASK, &signalset, NULL);
if (argc == 1 && euid == 0) if (argc == 1 && euid == 0)
{ {