linux-kernel - [PATCH 3.2 29/77] vfs: Make sendfile(2) killable even better

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <lsq.1450971462.257468965@decadent.org.uk>
Date:	Thu, 24 Dec 2015 15:37:42 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Al Viro" <viro@...iv.linux.org.uk>,
	"Dmitry Vyukov" <dvyukov@...gle.com>, "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.2 29/77] vfs: Make sendfile(2) killable even better

3.2.75-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit c725bfce7968009756ed2836a8cd7ba4dc163011 upstream.

Commit 296291cdd162 (mm: make sendfile(2) killable) fixed an issue where
sendfile(2) was doing a lot of tiny writes into a filesystem and thus
was unkillable for a long time. However sendfile(2) can be (mis)used to
issue lots of writes into arbitrary file descriptor such as evenfd or
similar special file descriptors which never hit the standard filesystem
write path and thus are still unkillable. E.g. the following example
from Dmitry burns CPU for ~16s on my test system without possibility to
be killed:

        int r1 = eventfd(0, 0);
        int r2 = memfd_create("", 0);
        unsigned long n = 1<<30;
        fallocate(r2, 0, 0, n);
        sendfile(r1, r2, 0, n);

There are actually quite a few tests for pending signals in sendfile
code however we data to write is always available none of them seems to
trigger. So fix the problem by adding a test for pending signal into
splice_from_pipe_next() also before the loop waiting for pipe buffers to
be available. This should fix all the lockup issues with sendfile of the
do-ton-of-tiny-writes nature.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/splice.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/fs/splice.c
+++ b/fs/splice.c
@@ -872,6 +872,13 @@ EXPORT_SYMBOL(splice_from_pipe_feed);
  */
 int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
 {
+	/*
+	 * Check for signal early to make process killable when there are
+	 * always buffers available
+	 */
+	if (signal_pending(current))
+		return -ERESTARTSYS;
+
 	while (!pipe->nrbufs) {
 		if (!pipe->writers)
 			return 0;

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/