linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Miklos Szeredi <mszeredi@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.4 02/26] af_unix: fix garbage collect vs MSG_PEEK
Date: Mon,  2 Aug 2021 15:44:12 +0200	[thread overview]
Message-ID: <20210802134332.110702961@linuxfoundation.org> (raw)
In-Reply-To: <20210802134332.033552261@linuxfoundation.org>

From: Miklos Szeredi <mszeredi@redhat.com>

commit cbcf01128d0a92e131bd09f1688fe032480b65ca upstream.

unix_gc() assumes that candidate sockets can never gain an external
reference (i.e.  be installed into an fd) while the unix_gc_lock is
held.  Except for MSG_PEEK this is guaranteed by modifying inflight
count under the unix_gc_lock.

MSG_PEEK does not touch any variable protected by unix_gc_lock (file
count is not), yet it needs to be serialized with garbage collection.
Do this by locking/unlocking unix_gc_lock:

 1) increment file count

 2) lock/unlock barrier to make sure incremented file count is visible
    to garbage collection

 3) install file into fd

This is a lock barrier (unlike smp_mb()) that ensures that garbage
collection is run completely before or completely after the barrier.

Cc: <stable@vger.kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/unix/af_unix.c |   51 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 49 insertions(+), 2 deletions(-)

--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1506,6 +1506,53 @@ out:
 	return err;
 }
 
+static void unix_peek_fds(struct scm_cookie *scm, struct sk_buff *skb)
+{
+	scm->fp = scm_fp_dup(UNIXCB(skb).fp);
+
+	/*
+	 * Garbage collection of unix sockets starts by selecting a set of
+	 * candidate sockets which have reference only from being in flight
+	 * (total_refs == inflight_refs).  This condition is checked once during
+	 * the candidate collection phase, and candidates are marked as such, so
+	 * that non-candidates can later be ignored.  While inflight_refs is
+	 * protected by unix_gc_lock, total_refs (file count) is not, hence this
+	 * is an instantaneous decision.
+	 *
+	 * Once a candidate, however, the socket must not be reinstalled into a
+	 * file descriptor while the garbage collection is in progress.
+	 *
+	 * If the above conditions are met, then the directed graph of
+	 * candidates (*) does not change while unix_gc_lock is held.
+	 *
+	 * Any operations that changes the file count through file descriptors
+	 * (dup, close, sendmsg) does not change the graph since candidates are
+	 * not installed in fds.
+	 *
+	 * Dequeing a candidate via recvmsg would install it into an fd, but
+	 * that takes unix_gc_lock to decrement the inflight count, so it's
+	 * serialized with garbage collection.
+	 *
+	 * MSG_PEEK is special in that it does not change the inflight count,
+	 * yet does install the socket into an fd.  The following lock/unlock
+	 * pair is to ensure serialization with garbage collection.  It must be
+	 * done between incrementing the file count and installing the file into
+	 * an fd.
+	 *
+	 * If garbage collection starts after the barrier provided by the
+	 * lock/unlock, then it will see the elevated refcount and not mark this
+	 * as a candidate.  If a garbage collection is already in progress
+	 * before the file count was incremented, then the lock/unlock pair will
+	 * ensure that garbage collection is finished before progressing to
+	 * installing the fd.
+	 *
+	 * (*) A -> B where B is on the queue of A or B is on the queue of C
+	 * which is on the queue of listening socket A.
+	 */
+	spin_lock(&unix_gc_lock);
+	spin_unlock(&unix_gc_lock);
+}
+
 static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)
 {
 	int err = 0;
@@ -2131,7 +2178,7 @@ static int unix_dgram_recvmsg(struct soc
 		sk_peek_offset_fwd(sk, size);
 
 		if (UNIXCB(skb).fp)
-			scm.fp = scm_fp_dup(UNIXCB(skb).fp);
+			unix_peek_fds(&scm, skb);
 	}
 	err = (flags & MSG_TRUNC) ? skb->len - skip : size;
 
@@ -2376,7 +2423,7 @@ unlock:
 			/* It is questionable, see note in unix_dgram_recvmsg.
 			 */
 			if (UNIXCB(skb).fp)
-				scm.fp = scm_fp_dup(UNIXCB(skb).fp);
+				unix_peek_fds(&scm, skb);
 
 			sk_peek_offset_fwd(sk, chunk);
 



  parent reply	other threads:[~2021-08-02 13:47 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02 13:44 [PATCH 4.4 00/26] 4.4.278-rc1 review Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 01/26] net: split out functions related to registering inflight socket files Greg Kroah-Hartman
2021-08-02 13:44 ` Greg Kroah-Hartman [this message]
2021-08-02 13:44 ` [PATCH 4.4 03/26] workqueue: fix UAF in pwq_unbound_release_workfn() Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 04/26] net/802/mrp: fix memleak in mrp_request_join() Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 05/26] net/802/garp: fix memleak in garp_request_join() Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 06/26] sctp: move 198 addresses from unusable to private scope Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 07/26] hfs: add missing clean-up in hfs_fill_super Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 08/26] hfs: fix high memory mapping in hfs_bnode_read Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 09/26] hfs: add lock nesting notation to hfs_find_init Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 10/26] ARM: dts: versatile: Fix up interrupt controller node names Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 11/26] lib/string.c: add multibyte memset functions Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 12/26] ARM: ensure the signal page contains defined contents Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 13/26] ocfs2: fix zero out valid data Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 14/26] ocfs2: issue zeroout to EOF blocks Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 15/26] can: usb_8dev: fix memory leak Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 16/26] can: ems_usb: " Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 17/26] can: esd_usb2: " Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 18/26] NIU: fix incorrect error return, missed in previous revert Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 19/26] x86/asm: Ensure asm/proto.h can be included stand-alone Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 20/26] cfg80211: Fix possible memory leak in function cfg80211_bss_update Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 21/26] netfilter: nft_nat: allow to specify layer 4 protocol NAT only Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 22/26] tipc: fix sleeping in tipc accept routine Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 23/26] mlx4: Fix missing error code in mlx4_load_one() Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 24/26] net: llc: fix skb_over_panic Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 25/26] tulip: windbond-840: Fix missing pci_disable_device() in probe and remove Greg Kroah-Hartman
2021-08-02 13:44 ` [PATCH 4.4 26/26] sis900: " Greg Kroah-Hartman
2021-08-02 17:51 ` [PATCH 4.4 00/26] 4.4.278-rc1 review Pavel Machek
2021-08-03 14:57 ` Naresh Kamboju
2021-08-03 19:14 ` Guenter Roeck

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210802134332.110702961@linuxfoundation.org \
    --to=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mszeredi@redhat.com \
    --cc=stable@vger.kernel.org \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [PATCH 4.4 02/26] af_unix: fix garbage collect vs MSG_PEEK' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).