file capabilities: don't prevent signaling setuid root programs
An unprivileged process must be able to kill a setuid root program started
by the same user. This is legacy behavior needed for instance for xinit to
kill X when the window manager exits.
When an unprivileged user runs a setuid root program in !SECURE_NOROOT
mode, fP, fI, and fE are set full on, so pP' and pE' are full on. Then
cap_task_kill() prevents the user from signaling the setuid root task.
This is a change in behavior compared to when
!CONFIG_SECURITY_FILE_CAPABILITIES.
This patch introduces a special check into cap_task_kill() just to check
whether a non-root user is signaling a setuid root program started by the
same user. If so, then signal is allowed.
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Andrew Morgan <morgan@kernel.org>
Cc: Stephen Smalley <sds@epoch.ncsc.mil>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: James Morris <jmorris@namei.org>
Cc: Casey Schaufler <casey@schaufler-ca.com>
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 302e8d0..5bc1895 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -526,6 +526,15 @@
if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
return 0;
+ /*
+ * Running a setuid root program raises your capabilities.
+ * Killing your own setuid root processes was previously
+ * allowed.
+ * We must preserve legacy signal behavior in this case.
+ */
+ if (p->euid == 0 && p->uid == current->uid)
+ return 0;
+
/* sigcont is permitted within same session */
if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p)))
return 0;