From nobody Sun Feb 8 00:11:15 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE7B0C6FA82 for ; Tue, 13 Sep 2022 14:21:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233381AbiIMOVA (ORCPT ); Tue, 13 Sep 2022 10:21:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233285AbiIMOSl (ORCPT ); Tue, 13 Sep 2022 10:18:41 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18008642FF; Tue, 13 Sep 2022 07:13:02 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CCB57614C4; Tue, 13 Sep 2022 14:13:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D52E3C433D6; Tue, 13 Sep 2022 14:13:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1663078382; bh=sMyoQojcLrwPQiRLId1q2CAA2F5uODHLeQKKouA9PPM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TUlgCjyxnTreZnwi9etSp/8ZPOshElgGXMCFss7v9d2nQ99BJa/gbLbPNRi+AScVa rS9CsH7ahxfSObnOzEUxmcMj1ZszR2AzF/jEgUfq8iYg7NeEphqa3/ypgfDOXeE1yb GyYfqq+g7Nf2odA6Oe1I+LoBkzSZCim6es09olSU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot , Eric Dumazet , Shakeel Butt , "David S. Miller" , Sasha Levin Subject: [PATCH 5.19 118/192] tcp: TX zerocopy should not sense pfmemalloc status Date: Tue, 13 Sep 2022 16:03:44 +0200 Message-Id: <20220913140415.863548926@linuxfoundation.org> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220913140410.043243217@linuxfoundation.org> References: <20220913140410.043243217@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Eric Dumazet [ Upstream commit 3261400639463a853ba2b3be8bd009c2a8089775 ] We got a recent syzbot report [1] showing a possible misuse of pfmemalloc page status in TCP zerocopy paths. Indeed, for pages coming from user space or other layers, using page_is_pfmemalloc() is moot, and possibly could give false positives. There has been attempts to make page_is_pfmemalloc() more robust, but not using it in the first place in this context is probably better, removing cpu cycles. Note to stable teams : You need to backport 84ce071e38a6 ("net: introduce __skb_fill_page_desc_noacc") as a prereq. Race is more probable after commit c07aea3ef4d4 ("mm: add a signature in struct page") because page_is_pfmemalloc() is now using low order bit from page->lru.next, which can change more often than page->index. Low order bit should never be set for lru.next (when used as an anchor in LRU list), so KCSAN report is mostly a false positive. Backporting to older kernel versions seems not necessary. [1] BUG: KCSAN: data-race in lru_add_fn / tcp_build_frag write to 0xffffea0004a1d2c8 of 8 bytes by task 18600 on cpu 0: __list_add include/linux/list.h:73 [inline] list_add include/linux/list.h:88 [inline] lruvec_add_folio include/linux/mm_inline.h:105 [inline] lru_add_fn+0x440/0x520 mm/swap.c:228 folio_batch_move_lru+0x1e1/0x2a0 mm/swap.c:246 folio_batch_add_and_move mm/swap.c:263 [inline] folio_add_lru+0xf1/0x140 mm/swap.c:490 filemap_add_folio+0xf8/0x150 mm/filemap.c:948 __filemap_get_folio+0x510/0x6d0 mm/filemap.c:1981 pagecache_get_page+0x26/0x190 mm/folio-compat.c:104 grab_cache_page_write_begin+0x2a/0x30 mm/folio-compat.c:116 ext4_da_write_begin+0x2dd/0x5f0 fs/ext4/inode.c:2988 generic_perform_write+0x1d4/0x3f0 mm/filemap.c:3738 ext4_buffered_write_iter+0x235/0x3e0 fs/ext4/file.c:270 ext4_file_write_iter+0x2e3/0x1210 call_write_iter include/linux/fs.h:2187 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x468/0x760 fs/read_write.c:578 ksys_write+0xe8/0x1a0 fs/read_write.c:631 __do_sys_write fs/read_write.c:643 [inline] __se_sys_write fs/read_write.c:640 [inline] __x64_sys_write+0x3e/0x50 fs/read_write.c:640 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd read to 0xffffea0004a1d2c8 of 8 bytes by task 18611 on cpu 1: page_is_pfmemalloc include/linux/mm.h:1740 [inline] __skb_fill_page_desc include/linux/skbuff.h:2422 [inline] skb_fill_page_desc include/linux/skbuff.h:2443 [inline] tcp_build_frag+0x613/0xb20 net/ipv4/tcp.c:1018 do_tcp_sendpages+0x3e8/0xaf0 net/ipv4/tcp.c:1075 tcp_sendpage_locked net/ipv4/tcp.c:1140 [inline] tcp_sendpage+0x89/0xb0 net/ipv4/tcp.c:1150 inet_sendpage+0x7f/0xc0 net/ipv4/af_inet.c:833 kernel_sendpage+0x184/0x300 net/socket.c:3561 sock_sendpage+0x5a/0x70 net/socket.c:1054 pipe_to_sendpage+0x128/0x160 fs/splice.c:361 splice_from_pipe_feed fs/splice.c:415 [inline] __splice_from_pipe+0x222/0x4d0 fs/splice.c:559 splice_from_pipe fs/splice.c:594 [inline] generic_splice_sendpage+0x89/0xc0 fs/splice.c:743 do_splice_from fs/splice.c:764 [inline] direct_splice_actor+0x80/0xa0 fs/splice.c:931 splice_direct_to_actor+0x305/0x620 fs/splice.c:886 do_splice_direct+0xfb/0x180 fs/splice.c:974 do_sendfile+0x3bf/0x910 fs/read_write.c:1249 __do_sys_sendfile64 fs/read_write.c:1317 [inline] __se_sys_sendfile64 fs/read_write.c:1303 [inline] __x64_sys_sendfile64+0x10c/0x150 fs/read_write.c:1303 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd value changed: 0x0000000000000000 -> 0xffffea0004a1d288 Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 18611 Comm: syz-executor.4 Not tainted 6.0.0-rc2-syzkaller-0024= 8-ge022620b5d05-dirty #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Goo= gle 07/22/2022 Fixes: c07aea3ef4d4 ("mm: add a signature in struct page") Reported-by: syzbot Signed-off-by: Eric Dumazet Cc: Shakeel Butt Reviewed-by: Shakeel Butt Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- include/linux/skbuff.h | 21 +++++++++++++++++++++ net/core/datagram.c | 2 +- net/ipv4/tcp.c | 2 +- 3 files changed, 23 insertions(+), 2 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index b0a1374043f30..63d0a21b63162 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2587,6 +2587,27 @@ static inline void skb_fill_page_desc(struct sk_buff= *skb, int i, skb_shinfo(skb)->nr_frags =3D i + 1; } =20 +/** + * skb_fill_page_desc_noacc - initialise a paged fragment in an skb + * @skb: buffer containing fragment to be initialised + * @i: paged fragment index to initialise + * @page: the page to use for this fragment + * @off: the offset to the data with @page + * @size: the length of the data + * + * Variant of skb_fill_page_desc() which does not deal with + * pfmemalloc, if page is not owned by us. + */ +static inline void skb_fill_page_desc_noacc(struct sk_buff *skb, int i, + struct page *page, int off, + int size) +{ + struct skb_shared_info *shinfo =3D skb_shinfo(skb); + + __skb_fill_page_desc_noacc(shinfo, i, page, off, size); + shinfo->nr_frags =3D i + 1; +} + void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int of= f, int size, unsigned int truesize); =20 diff --git a/net/core/datagram.c b/net/core/datagram.c index 50f4faeea76cc..48e82438acb02 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -675,7 +675,7 @@ int __zerocopy_sg_from_iter(struct sock *sk, struct sk_= buff *skb, page_ref_sub(last_head, refs); refs =3D 0; } - skb_fill_page_desc(skb, frag++, head, start, size); + skb_fill_page_desc_noacc(skb, frag++, head, start, size); } if (refs) page_ref_sub(last_head, refs); diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 3d446773ff2a5..ab03977b65781 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1015,7 +1015,7 @@ static struct sk_buff *tcp_build_frag(struct sock *sk= , int size_goal, int flags, skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy); } else { get_page(page); - skb_fill_page_desc(skb, i, page, offset, copy); + skb_fill_page_desc_noacc(skb, i, page, offset, copy); } =20 if (!(flags & MSG_NO_SHARED_FRAGS)) --=20 2.35.1