73 lines
2.4 KiB
Diff
73 lines
2.4 KiB
Diff
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Fix CVE-2017-2616:
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https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-2616
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http://seclists.org/oss-sec/2017/q1/490
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http://seclists.org/oss-sec/2017/q1/474
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Patch copied from upstream source repository:
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https://github.com/shadow-maint/shadow/commit/08fd4b69e84364677a10e519ccb25b71710ee686
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From 08fd4b69e84364677a10e519ccb25b71710ee686 Mon Sep 17 00:00:00 2001
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From: Tobias Stoeckmann <tobias@stoeckmann.org>
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Date: Thu, 23 Feb 2017 09:47:29 -0600
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Subject: [PATCH] su: properly clear child PID
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If su is compiled with PAM support, it is possible for any local user
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to send SIGKILL to other processes with root privileges. There are
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only two conditions. First, the user must be able to perform su with
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a successful login. This does NOT have to be the root user, even using
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su with the same id is enough, e.g. "su $(whoami)". Second, SIGKILL
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can only be sent to processes which were executed after the su process.
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It is not possible to send SIGKILL to processes which were already
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running. I consider this as a security vulnerability, because I was
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able to write a proof of concept which unlocked a screen saver of
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another user this way.
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---
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src/su.c | 19 +++++++++++++++++--
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1 file changed, 17 insertions(+), 2 deletions(-)
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diff --git a/src/su.c b/src/su.c
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index f20d230..d86aa86 100644
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--- a/src/su.c
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+++ b/src/su.c
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@@ -379,11 +379,13 @@ static void prepare_pam_close_session (void)
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/* wake child when resumed */
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kill (pid, SIGCONT);
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stop = false;
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+ } else {
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+ pid_child = 0;
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}
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} while (!stop);
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}
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- if (0 != caught) {
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+ if (0 != caught && 0 != pid_child) {
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(void) fputs ("\n", stderr);
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(void) fputs (_("Session terminated, terminating shell..."),
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stderr);
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@@ -393,9 +395,22 @@ static void prepare_pam_close_session (void)
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snprintf (wait_msg, sizeof wait_msg, _(" ...waiting for child to terminate.\n"));
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(void) signal (SIGALRM, kill_child);
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+ (void) signal (SIGCHLD, catch_signals);
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(void) alarm (2);
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- (void) wait (&status);
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+ sigemptyset (&ourset);
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+ if ((sigaddset (&ourset, SIGALRM) != 0)
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+ || (sigprocmask (SIG_BLOCK, &ourset, NULL) != 0)) {
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+ fprintf (stderr, _("%s: signal masking malfunction\n"), Prog);
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+ kill_child (0);
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+ } else {
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+ while (0 == waitpid (pid_child, &status, WNOHANG)) {
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+ sigsuspend (&ourset);
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+ }
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+ pid_child = 0;
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+ (void) sigprocmask (SIG_UNBLOCK, &ourset, NULL);
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+ }
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+
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(void) fputs (_(" ...terminated.\n"), stderr);
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}
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