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Date: Fri, 15 Mar 2024 21:15:19 +0100
From: Greg Kroah-Hartman <>
Cc: Greg Kroah-Hartman <>
Subject: CVE-2021-47129: netfilter: nft_ct: skip expectations for confirmed conntrack


In the Linux kernel, the following vulnerability has been resolved:

netfilter: nft_ct: skip expectations for confirmed conntrack

nft_ct_expect_obj_eval() calls nf_ct_ext_add() for a confirmed
conntrack entry. However, nf_ct_ext_add() can only be called for

[ 1825.349056] WARNING: CPU: 0 PID: 1279 at net/netfilter/nf_conntrack_extend.c:48 nf_ct_xt_add+0x18e/0x1a0 [nf_conntrack]
[ 1825.351391] RIP: 0010:nf_ct_ext_add+0x18e/0x1a0 [nf_conntrack]
[ 1825.351493] Code: 41 5c 41 5d 41 5e 41 5f c3 41 bc 0a 00 00 00 e9 15 ff ff ff ba 09 00 00 00 31 f6 4c 89 ff e8 69 6c 3d e9 eb 96 45 31 ed eb cd <0f> 0b e9 b1 fe ff ff e8 86 79 14 e9 eb bf 0f 1f 40 00 0f 1f 44 00
[ 1825.351721] RSP: 0018:ffffc90002e1f1e8 EFLAGS: 00010202
[ 1825.351790] RAX: 000000000000000e RBX: ffff88814f5783c0 RCX: ffffffffc0e4f887
[ 1825.351881] RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88814f578440
[ 1825.351971] RBP: 0000000000000000 R08: 0000000000000000 R09: ffff88814f578447
[ 1825.352060] R10: ffffed1029eaf088 R11: 0000000000000001 R12: ffff88814f578440
[ 1825.352150] R13: ffff8882053f3a00 R14: 0000000000000000 R15: 0000000000000a20
[ 1825.352240] FS:  00007f992261c900(0000) GS:ffff889faec00000(0000) knlGS:0000000000000000
[ 1825.352343] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1825.352417] CR2: 000056070a4d1158 CR3: 000000015efe0000 CR4: 0000000000350ee0
[ 1825.352508] Call Trace:
[ 1825.352544]  nf_ct_helper_ext_add+0x10/0x60 [nf_conntrack]
[ 1825.352641]  nft_ct_expect_obj_eval+0x1b8/0x1e0 [nft_ct]
[ 1825.352716]  nft_do_chain+0x232/0x850 [nf_tables]

Add the ct helper extension only for unconfirmed conntrack. Skip rule
evaluation if the ct helper extension does not exist. Thus, you can
only create expectations from the first packet.

It should be possible to remove this limitation by adding a new action
to attach a generic ct helper to the first packet. Then, use this ct
helper extension from follow up packets to create the ct expectation.

While at it, add a missing check to skip the template conntrack too
and remove check for IPCT_UNTRACK which is implicit to !ct.

The Linux kernel CVE team has assigned CVE-2021-47129 to this issue.

Affected and fixed versions

	Issue introduced in 5.3 with commit 857b46027d6f and fixed in 5.4.125 with commit da8d31e80ff4
	Issue introduced in 5.3 with commit 857b46027d6f and fixed in 5.10.43 with commit 5f3429c05e40
	Issue introduced in 5.3 with commit 857b46027d6f and fixed in 5.12.10 with commit 2c0e6b35b88a
	Issue introduced in 5.3 with commit 857b46027d6f and fixed in 5.13 with commit 1710eb913bdc

Please see or a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files

The file(s) affected by this issue are:


The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:

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