From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 72B6D4FECE1; Wed, 30 Sep 2026 15:59:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790783999; cv=none; b=WMu8/kvEC6ZkbRADJPLBuaAU8KpeNq6RrhPeWJB3DqCQCLeLlhY5Jhqinucj1wvDHJ/4AUhLJy/YvSNeoBDVG1si0jIpLQEpEgZiMR4J/CVrWBMaVINh7HPUC93AbRAUtdxvvn/bFDl7o3hJaMtT25Wz1efsC9HhK9/uSzXfvCc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790783999; c=relaxed/simple; bh=8+El5h8h+MPIejCPIiV7SefBEI/n4Aia57+JaZ+u0Cs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cb5kaikeQFmaTt50VBlVdmWmpl1EMjVfJqb0X3dsTilpOmwpozkFrf5JDzgwgYpkRqdioRueBjGUlMdWO8sB8JZBYPSpim/lyxxgRarjzROVXzkBHuHSN36d+qpng8SEnnL5XzzhrrKVgzgJpbFv2r3sMRW9wWrJZHhpeO4J3pA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=B3ArRKW2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="B3ArRKW2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2855B1F00893; Wed, 30 Sep 2026 15:59:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790783994; bh=tVOePGsD2aZTBFvdoiU/sq/igZ4eD1oG3+B16CFGPUA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=B3ArRKW2JbkXm30ldGGoMpCkQT9Wsoov8Oe/DMW3MKtiv982FwmY2fPMEWGKeilKY J6AFl3wHmVMxTJYfTpwKznb52HMHT1K2inJ7EOU0uugUOdt6aZ1TotiYdCars6PZ7W 4Oe7j+8EmMW6ELEEl7FENlY1Qdu5ISmWUFaXGQrs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot , Eric Dumazet , Marco Elver , Jakub Kicinski , "Miguel Gazquez (Schneider Electric)" , Sasha Levin Subject: [PATCH 5.10 550/595] net: preserve skb_end_offset() in skb_unclone_keeptruesize() Date: Wed, 30 Sep 2026 17:27:23 +0200 Message-ID: <20260930152359.544611168@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152347.700140858@linuxfoundation.org> References: <20260930152347.700140858@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit 2b88cba55883eaafbc9b7cbff0b2c7cdba71ed01 upstream. syzbot found another way to trigger the infamous WARN_ON_ONCE(delta < len) in skb_try_coalesce() [1] I was able to root cause the issue to kfence. When kfence is in action, the following assertion is no longer true: int size = xxxx; void *ptr1 = kmalloc(size, gfp); void *ptr2 = kmalloc(size, gfp); if (ptr1 && ptr2) ASSERT(ksize(ptr1) == ksize(ptr2)); We attempted to fix these issues in the blamed commits, but forgot that TCP was possibly shifting data after skb_unclone_keeptruesize() has been used, notably from tcp_retrans_try_collapse(). So we not only need to keep same skb->truesize value, we also need to make sure TCP wont fill new tailroom that pskb_expand_head() was able to get from a addr = kmalloc(...) followed by ksize(addr) Split skb_unclone_keeptruesize() into two parts: 1) Inline skb_unclone_keeptruesize() for the common case, when skb is not cloned. 2) Out of line __skb_unclone_keeptruesize() for the 'slow path'. WARNING: CPU: 1 PID: 6490 at net/core/skbuff.c:5295 skb_try_coalesce+0x1235/0x1560 net/core/skbuff.c:5295 Modules linked in: CPU: 1 PID: 6490 Comm: syz-executor161 Not tainted 5.17.0-rc4-syzkaller-00229-g4f12b742eb2b #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:skb_try_coalesce+0x1235/0x1560 net/core/skbuff.c:5295 Code: bf 01 00 00 00 0f b7 c0 89 c6 89 44 24 20 e8 62 24 4e fa 8b 44 24 20 83 e8 01 0f 85 e5 f0 ff ff e9 87 f4 ff ff e8 cb 20 4e fa <0f> 0b e9 06 f9 ff ff e8 af b2 95 fa e9 69 f0 ff ff e8 95 b2 95 fa RSP: 0018:ffffc900063af268 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 00000000ffffffd5 RCX: 0000000000000000 RDX: ffff88806fc05700 RSI: ffffffff872abd55 RDI: 0000000000000003 RBP: ffff88806e675500 R08: 00000000ffffffd5 R09: 0000000000000000 R10: ffffffff872ab659 R11: 0000000000000000 R12: ffff88806dd554e8 R13: ffff88806dd9bac0 R14: ffff88806dd9a2c0 R15: 0000000000000155 FS: 00007f18014f9700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020002000 CR3: 000000006be7a000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: tcp_try_coalesce net/ipv4/tcp_input.c:4651 [inline] tcp_try_coalesce+0x393/0x920 net/ipv4/tcp_input.c:4630 tcp_queue_rcv+0x8a/0x6e0 net/ipv4/tcp_input.c:4914 tcp_data_queue+0x11fd/0x4bb0 net/ipv4/tcp_input.c:5025 tcp_rcv_established+0x81e/0x1ff0 net/ipv4/tcp_input.c:5947 tcp_v4_do_rcv+0x65e/0x980 net/ipv4/tcp_ipv4.c:1719 sk_backlog_rcv include/net/sock.h:1037 [inline] __release_sock+0x134/0x3b0 net/core/sock.c:2779 release_sock+0x54/0x1b0 net/core/sock.c:3311 sk_wait_data+0x177/0x450 net/core/sock.c:2821 tcp_recvmsg_locked+0xe28/0x1fd0 net/ipv4/tcp.c:2457 tcp_recvmsg+0x137/0x610 net/ipv4/tcp.c:2572 inet_recvmsg+0x11b/0x5e0 net/ipv4/af_inet.c:850 sock_recvmsg_nosec net/socket.c:948 [inline] sock_recvmsg net/socket.c:966 [inline] sock_recvmsg net/socket.c:962 [inline] ____sys_recvmsg+0x2c4/0x600 net/socket.c:2632 ___sys_recvmsg+0x127/0x200 net/socket.c:2674 __sys_recvmsg+0xe2/0x1a0 net/socket.c:2704 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae Fixes: c4777efa751d ("net: add and use skb_unclone_keeptruesize() helper") Fixes: 097b9146c0e2 ("net: fix up truesize of cloned skb in skb_prepare_for_shift()") Reported-by: syzbot Signed-off-by: Eric Dumazet Cc: Marco Elver Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Signed-off-by: Miguel Gazquez (Schneider Electric) Signed-off-by: Sasha Levin --- include/linux/skbuff.h | 18 +++++++++--------- net/core/skbuff.c | 32 ++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 9 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 34b6a7e3af8d8..0a7b1a7f1ae10 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1655,19 +1655,19 @@ static inline int skb_unclone(struct sk_buff *skb, gfp_t pri) return 0; } -/* This variant of skb_unclone() makes sure skb->truesize is not changed */ +/* This variant of skb_unclone() makes sure skb->truesize + * and skb_end_offset() are not changed, whenever a new skb->head is needed. + * + * Indeed there is no guarantee that ksize(kmalloc(X)) == ksize(kmalloc(X)) + * when various debugging features are in place. + */ +int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri); static inline int skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri) { might_sleep_if(gfpflags_allow_blocking(pri)); - if (skb_cloned(skb)) { - unsigned int save = skb->truesize; - int res; - - res = pskb_expand_head(skb, 0, 0, pri); - skb->truesize = save; - return res; - } + if (skb_cloned(skb)) + return __skb_unclone_keeptruesize(skb, pri); return 0; } diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 39ecb52f507c9..224348001368c 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1737,6 +1737,38 @@ struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom) } EXPORT_SYMBOL(skb_realloc_headroom); +int __skb_unclone_keeptruesize(struct sk_buff *skb, gfp_t pri) +{ + unsigned int saved_end_offset, saved_truesize; + struct skb_shared_info *shinfo; + int res; + + saved_end_offset = skb_end_offset(skb); + saved_truesize = skb->truesize; + + res = pskb_expand_head(skb, 0, 0, pri); + if (res) + return res; + + skb->truesize = saved_truesize; + + if (likely(skb_end_offset(skb) == saved_end_offset)) + return 0; + + shinfo = skb_shinfo(skb); + + /* We are about to change back skb->end, + * we need to move skb_shinfo() to its new location. + */ + memmove(skb->head + saved_end_offset, + shinfo, + offsetof(struct skb_shared_info, frags[shinfo->nr_frags])); + + skb_set_end_offset(skb, saved_end_offset); + + return 0; +} + /** * skb_expand_head - reallocate header of &sk_buff * @skb: buffer to reallocate -- 2.53.0