From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D313A8801; Tue, 30 Apr 2024 11:20:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714476027; cv=none; b=Kz1mrN0RDYrFnBgKBt8dgz166/8iABGfLB4udbsaDLWNQVymMDQjNpnTnYFv2U7ypQy+Ksr56U5d9CgPYlHxosTLlLvKPMQqg1sp8YFaXrL9OEXe3lVumm5tFol8KlDyW0lTDiVJ2n/ctrTomw2UF8EVwB9lcqbE6B+N+VdFMKg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714476027; c=relaxed/simple; bh=HG+xaooJnka6EGocvSGdM2tYQgRiex6PckWEF2qmGZY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SPK9eCPcjlq+i+t+q5I6sVwUKq6FbcDa4NqA61dgP0HG9XlesKhqOzl//dn1T8Q0BHhLmujPi3iIr7acVtjfNo+jY9fdpw6EgjNesnEi4pYZnFcMqlGpVc/zMXRGC9gzFjKB9geNbyXFfhy5y4gxJkcOdyd+09UWMSeHZgU7zAc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=U5XdwdWO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="U5XdwdWO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3FCDDC2BBFC; Tue, 30 Apr 2024 11:20:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1714476027; bh=HG+xaooJnka6EGocvSGdM2tYQgRiex6PckWEF2qmGZY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U5XdwdWOXjRYwIsinT12Jv7uWs2L0eJPzJvfzzHUx4ecr6HOdHS3qc8L7dYEkeV3h gPqDeTPdLnGh+0JApq4U/VKcwF/7Eo7Qercuqafyb5m06Mw+RU4Fo+Q+OhDxGlRJz9 nUwPhFnuhKv/Ko+LhqMA6hMjiqS3FtteorYsFBO0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Michal Luczaj , Kuniyuki Iwashima , Paolo Abeni , Sasha Levin Subject: [PATCH 5.4 012/107] af_unix: Fix garbage collector racing against connect() Date: Tue, 30 Apr 2024 12:39:32 +0200 Message-ID: <20240430103045.023808647@linuxfoundation.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240430103044.655968143@linuxfoundation.org> References: <20240430103044.655968143@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michal Luczaj [ Upstream commit 47d8ac011fe1c9251070e1bd64cb10b48193ec51 ] Garbage collector does not take into account the risk of embryo getting enqueued during the garbage collection. If such embryo has a peer that carries SCM_RIGHTS, two consecutive passes of scan_children() may see a different set of children. Leading to an incorrectly elevated inflight count, and then a dangling pointer within the gc_inflight_list. sockets are AF_UNIX/SOCK_STREAM S is an unconnected socket L is a listening in-flight socket bound to addr, not in fdtable V's fd will be passed via sendmsg(), gets inflight count bumped connect(S, addr) sendmsg(S, [V]); close(V) __unix_gc() ---------------- ------------------------- ----------- NS = unix_create1() skb1 = sock_wmalloc(NS) L = unix_find_other(addr) unix_state_lock(L) unix_peer(S) = NS // V count=1 inflight=0 NS = unix_peer(S) skb2 = sock_alloc() skb_queue_tail(NS, skb2[V]) // V became in-flight // V count=2 inflight=1 close(V) // V count=1 inflight=1 // GC candidate condition met for u in gc_inflight_list: if (total_refs == inflight_refs) add u to gc_candidates // gc_candidates={L, V} for u in gc_candidates: scan_children(u, dec_inflight) // embryo (skb1) was not // reachable from L yet, so V's // inflight remains unchanged __skb_queue_tail(L, skb1) unix_state_unlock(L) for u in gc_candidates: if (u.inflight) scan_children(u, inc_inflight_move_tail) // V count=1 inflight=2 (!) If there is a GC-candidate listening socket, lock/unlock its state. This makes GC wait until the end of any ongoing connect() to that socket. After flipping the lock, a possibly SCM-laden embryo is already enqueued. And if there is another embryo coming, it can not possibly carry SCM_RIGHTS. At this point, unix_inflight() can not happen because unix_gc_lock is already taken. Inflight graph remains unaffected. Fixes: 1fd05ba5a2f2 ("[AF_UNIX]: Rewrite garbage collector, fixes race.") Signed-off-by: Michal Luczaj Reviewed-by: Kuniyuki Iwashima Link: https://lore.kernel.org/r/20240409201047.1032217-1-mhal@rbox.co Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- net/unix/garbage.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/net/unix/garbage.c b/net/unix/garbage.c index 675fbe594dbb3..58525311e903a 100644 --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -235,11 +235,22 @@ void unix_gc(void) * receive queues. Other, non candidate sockets _can_ be * added to queue, so we must make sure only to touch * candidates. + * + * Embryos, though never candidates themselves, affect which + * candidates are reachable by the garbage collector. Before + * being added to a listener's queue, an embryo may already + * receive data carrying SCM_RIGHTS, potentially making the + * passed socket a candidate that is not yet reachable by the + * collector. It becomes reachable once the embryo is + * enqueued. Therefore, we must ensure that no SCM-laden + * embryo appears in a (candidate) listener's queue between + * consecutive scan_children() calls. */ list_for_each_entry_safe(u, next, &gc_inflight_list, link) { + struct sock *sk = &u->sk; long total_refs; - total_refs = file_count(u->sk.sk_socket->file); + total_refs = file_count(sk->sk_socket->file); BUG_ON(!u->inflight); BUG_ON(total_refs < u->inflight); @@ -247,6 +258,11 @@ void unix_gc(void) list_move_tail(&u->link, &gc_candidates); __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags); __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags); + + if (sk->sk_state == TCP_LISTEN) { + unix_state_lock(sk); + unix_state_unlock(sk); + } } } -- 2.43.0