file capabilities: allow sigcont within session

Fix http://bugzilla.kernel.org/show_bug.cgi?id=9247

Allow sigcont to be sent to a process with greater capabilities if it is in
the same session.  Otherwise, a shell from which I've started a root shell
and done 'suspend' can't be restarted by the parent shell.

Also don't do file-capabilities signaling checks when uids for the
processes don't match, since the standard check_kill_permission will have
done those checks.

[akpm@linux-foundation.org: coding-style cleanups]
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Acked-by: Andrew Morgan <morgan@kernel.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Tested-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Stephen Smalley <sds@epoch.ncsc.mil>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: James Morris <jmorris@namei.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/security/commoncap.c b/security/commoncap.c
index bf67871..302e8d0 100644 (file)
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -526,6 +526,10 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info,
        if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
                return 0;
 
+       /* sigcont is permitted within same session */
+       if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p)))
+               return 0;
+
        if (secid)
                /*
                 * Signal sent as a particular user.