linux-kernel - [PATCH 2/2] signals: send_sigio: use do_send_sig_info() to avoid check_kill

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Message-ID: <20090801012838.GC30259@redhat.com>
Date:	Sat, 1 Aug 2009 03:28:38 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, eranian@...il.com,
	mingo@...e.hu, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	robert.richter@....com, paulus@...ba.org, andi@...stfloor.org,
	mpjohn@...ibm.com, cel@...ibm.com, cjashfor@...ibm.com,
	mucci@...s.utk.edu, terpstra@...s.utk.edu,
	perfmon2-devel@...ts.sourceforge.net, mtk.manpages@...glemail.com,
	roland@...hat.com
Subject: [PATCH 2/2] signals: send_sigio: use do_send_sig_info() to avoid
	check_kill_permission()

group_send_sig_info()->check_kill_permission() assumes that current
is the sender and uses current_cred().

This is not true in send_sigio_to_task() case. From the security pov
the sender is not current, but the task which did fcntl(F_SETOWN),
that is why we have sigio_perm() which uses the right creds to check.

Fortunately, send_sigio() always sends either SEND_SIG_PRIV or
SI_FROMKERNEL() signal, so check_kill_permission() does nothing. But
still it would be tidier to avoid this bogus security check and save
a couple of cycles.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 fs/fcntl.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- WAIT/fs/fcntl.c~2_SIGIO	2009-06-17 14:11:26.000000000 +0200
+++ WAIT/fs/fcntl.c	2009-08-01 02:40:41.000000000 +0200
@@ -462,11 +462,11 @@ static void send_sigio_to_task(struct ta
 			else
 				si.si_band = band_table[reason - POLL_IN];
 			si.si_fd    = fd;
-			if (!group_send_sig_info(signum, &si, p))
+			if (!do_send_sig_info(signum, &si, p, true))
 				break;
 		/* fall-through: fall back on the old plain SIGIO signal */
 		case 0:
-			group_send_sig_info(SIGIO, SEND_SIG_PRIV, p);
+			do_send_sig_info(SIGIO, SEND_SIG_PRIV, p, true);
 	}
 }
 

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