linux-kernel - Re: F_SETOWN_TID: F_SETOWN was thread-specific for a while

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Message-ID: <20090817174001.GA17535@redhat.com>
Date:	Mon, 17 Aug 2009 19:40:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	stephane eranian <eranian@...glemail.com>
Cc:	Jamie Lokier <jamie@...reable.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, 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: Re: F_SETOWN_TID: F_SETOWN was thread-specific for a while

Forgot to show the patch,

On 08/17, Oleg Nesterov wrote:
>
> And again, this is even documented. The change is trivial but user-space
> visible, it may confuse the (stupid) app which uses SIGIO + SA_SIGINFO
> without F_SETSIG.

Oleg.

Personally I do not really think this change is good idea. (and in any
case it should be re-diffed on top of Peter's OWN_EX patch).

Btw. _in theory_, "case 0" is not right wrt security_file_send_sigiotask(sig).
I think we shouldn't worry.

--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -431,6 +431,7 @@ static void send_sigio_to_task(struct ta
 			       int fd,
 			       int reason)
 {
+	siginfo_t si;
 	/*
 	 * F_SETSIG can change ->signum lockless in parallel, make
 	 * sure we read it once and use the same value throughout.
@@ -439,33 +440,33 @@ static void send_sigio_to_task(struct ta
 
 	if (!sigio_perm(p, fown, signum))
 		return;
+	/* Queue a rt signal with the appropriate fd as its
+	   value.  We use SI_SIGIO as the source, not 
+	   SI_KERNEL, since kernel signals always get 
+	   delivered even if we can't queue.  Failure to
+	   queue in this case _should_ be reported; we fall
+	   back to SIGIO in that case. --sct */
+	si.si_errno = 0;
+	si.si_fd    = fd;
+	si.si_code  = reason;
+	/* Make sure we are called with one of the POLL_*
+	   reasons, otherwise we could leak kernel stack into
+	   userspace.  */
+	BUG_ON((reason & __SI_MASK) != __SI_POLL);
+	if (reason - POLL_IN >= NSIGPOLL)
+		si.si_band  = ~0L;
+	else
+		si.si_band = band_table[reason - POLL_IN];
 
 	switch (signum) {
-		siginfo_t si;
 		default:
-			/* Queue a rt signal with the appropriate fd as its
-			   value.  We use SI_SIGIO as the source, not 
-			   SI_KERNEL, since kernel signals always get 
-			   delivered even if we can't queue.  Failure to
-			   queue in this case _should_ be reported; we fall
-			   back to SIGIO in that case. --sct */
 			si.si_signo = signum;
-			si.si_errno = 0;
-		        si.si_code  = reason;
-			/* Make sure we are called with one of the POLL_*
-			   reasons, otherwise we could leak kernel stack into
-			   userspace.  */
-			BUG_ON((reason & __SI_MASK) != __SI_POLL);
-			if (reason - POLL_IN >= NSIGPOLL)
-				si.si_band  = ~0L;
-			else
-				si.si_band = band_table[reason - POLL_IN];
-			si.si_fd    = fd;
 			if (!group_send_sig_info(signum, &si, p))
 				break;
 		/* fall-through: fall back on the old plain SIGIO signal */
 		case 0:
-			group_send_sig_info(SIGIO, SEND_SIG_PRIV, p);
+			si.si_signo = SIGIO;
+			group_send_sig_info(SIGIO, &si, p);
 	}
 }
 

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