From 39fd33933b0209e4b6254743f2cede07c5ad4c52 Mon Sep 17 00:00:00 2001 From: "Serge E. Hallyn" Date: Wed, 23 Mar 2011 16:43:19 -0700 Subject: [PATCH] userns: allow killing tasks in your own or child userns Changelog: Dec 8: Fixed bug in my check_kill_permission pointed out by Eric Biederman. Dec 13: Apply Eric's suggestion to pass target task into kill_ok_by_cred() for clarity Dec 31: address comment by Eric Biederman: don't need cred/tcred in check_kill_permission. Jan 1: use const cred struct. Jan 11: Per Bastian Blank's advice, clean up kill_ok_by_cred(). Feb 16: kill_ok_by_cred: fix bad parentheses Feb 23: per akpm, let compiler inline kill_ok_by_cred Signed-off-by: Serge E. Hallyn Acked-by: "Eric W. Biederman" Acked-by: Daniel Lezcano Acked-by: David Howells Cc: James Morris Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/signal.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 31751868de8..324eff5468a 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -635,6 +635,27 @@ static inline bool si_fromuser(const struct siginfo *info) (!is_si_special(info) && SI_FROMUSER(info)); } +/* + * called with RCU read lock from check_kill_permission() + */ +static int kill_ok_by_cred(struct task_struct *t) +{ + const struct cred *cred = current_cred(); + const struct cred *tcred = __task_cred(t); + + if (cred->user->user_ns == tcred->user->user_ns && + (cred->euid == tcred->suid || + cred->euid == tcred->uid || + cred->uid == tcred->suid || + cred->uid == tcred->uid)) + return 1; + + if (ns_capable(tcred->user->user_ns, CAP_KILL)) + return 1; + + return 0; +} + /* * Bad permissions for sending the signal * - the caller must hold the RCU read lock @@ -642,7 +663,6 @@ static inline bool si_fromuser(const struct siginfo *info) static int check_kill_permission(int sig, struct siginfo *info, struct task_struct *t) { - const struct cred *cred, *tcred; struct pid *sid; int error; @@ -656,14 +676,8 @@ static int check_kill_permission(int sig, struct siginfo *info, if (error) return error; - cred = current_cred(); - tcred = __task_cred(t); if (!same_thread_group(current, t) && - (cred->euid ^ tcred->suid) && - (cred->euid ^ tcred->uid) && - (cred->uid ^ tcred->suid) && - (cred->uid ^ tcred->uid) && - !capable(CAP_KILL)) { + !kill_ok_by_cred(t)) { switch (sig) { case SIGCONT: sid = task_session(t); -- 2.20.1