diff options
Diffstat (limited to 'source/a/shadow/shadow.CVE-2017-2616.diff')
-rw-r--r-- | source/a/shadow/shadow.CVE-2017-2616.diff | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/source/a/shadow/shadow.CVE-2017-2616.diff b/source/a/shadow/shadow.CVE-2017-2616.diff new file mode 100644 index 00000000..4a5c4422 --- /dev/null +++ b/source/a/shadow/shadow.CVE-2017-2616.diff @@ -0,0 +1,55 @@ +su: properly clear child PID + +If su is compiled with PAM support, it is possible for any local user +to send SIGKILL to other processes with root privileges. There are +only two conditions. First, the user must be able to perform su with +a successful login. This does NOT have to be the root user, even using +su with the same id is enough, e.g. "su $(whoami)". Second, SIGKILL +can only be sent to processes which were executed after the su process. +It is not possible to send SIGKILL to processes which were already +running. I consider this as a security vulnerability, because I was +able to write a proof of concept which unlocked a screen saver of +another user this way. + +diff --git a/src/su.c b/src/su.c +index f20d230..d86aa86 100644 +--- a/src/su.c ++++ b/src/su.c +@@ -379,11 +379,13 @@ static void prepare_pam_close_session (void) + /* wake child when resumed */ + kill (pid, SIGCONT); + stop = false; ++ } else { ++ pid_child = 0; + } + } while (!stop); + } + +- if (0 != caught) { ++ if (0 != caught && 0 != pid_child) { + (void) fputs ("\n", stderr); + (void) fputs (_("Session terminated, terminating shell..."), + stderr); +@@ -393,9 +395,22 @@ static void prepare_pam_close_session (void) + snprintf (wait_msg, sizeof wait_msg, _(" ...waiting for child to terminate.\n")); + + (void) signal (SIGALRM, kill_child); ++ (void) signal (SIGCHLD, catch_signals); + (void) alarm (2); + +- (void) wait (&status); ++ sigemptyset (&ourset); ++ if ((sigaddset (&ourset, SIGALRM) != 0) ++ || (sigprocmask (SIG_BLOCK, &ourset, NULL) != 0)) { ++ fprintf (stderr, _("%s: signal masking malfunction\n"), Prog); ++ kill_child (0); ++ } else { ++ while (0 == waitpid (pid_child, &status, WNOHANG)) { ++ sigsuspend (&ourset); ++ } ++ pid_child = 0; ++ (void) sigprocmask (SIG_UNBLOCK, &ourset, NULL); ++ } ++ + (void) fputs (_(" ...terminated.\n"), stderr); + } |