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netfilter: nft_socket: make cgroupsv2 matching work with namespaces

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When running in container environmment, /sys/fs/cgroup/ might not be
the real root node of the sk-attached cgroup.

Example:

In container:
% stat /sys//fs/cgroup/
Device: 0,21    Inode: 2214  ..
% stat /sys/fs/cgroup/foo
Device: 0,21    Inode: 2264  ..

The expectation would be for:

  nft add rule .. socket cgroupv2 level 1 "foo" counter

to match traffic from a process that got added to "foo" via
"echo $pid > /sys/fs/cgroup/foo/cgroup.procs".

However, 'level 3' is needed to make this work.

Seen from initial namespace, the complete hierarchy is:

% stat /sys/fs/cgroup/system.slice/docker-.../foo
  Device: 0,21    Inode: 2264 ..

i.e. hierarchy is
0    1               2              3
/ -> system.slice -> docker-1... -> foo

... but the container doesn't know that its "/" is the "docker-1.."
cgroup.  Current code will retrieve the 'system.slice' cgroup node
and store its kn->id in the destination register, so compare with
2264 ("foo" cgroup id) will not match.

Fetch "/" cgroup from ->init() and add its level to the level we try to
extract.  cgroup root-level is 0 for the init-namespace or the level
of the ancestor that is exposed as the cgroup root inside the container.

In the above case, cgrp->level of "/" resolved in the container is 2
(docker-1...scope/) and request for 'level 1' will get adjusted
to fetch the actual level (3).

v2: use CONFIG_SOCK_CGROUP_DATA, eval function depends on it.
    (kernel test robot)

Cc: cgroups@vger.kernel.org
Fixes: e0bb96db96 ("netfilter: nft_socket: add support for cgroupsv2")
Reported-by: Nadia Pinaeva <n.m.pinaeva@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2024-09-07 16:07:49 +02:00 committed by Pablo Neira Ayuso
parent 8b26ff7af8
commit 7f3287db65
1 changed files with 38 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

41
net/netfilter/nft_socket.c
View file

@ -9,7 +9,8 @@
struct nft_socket {
enum nft_socket_keys key:8;
u8 level;
u8 level; /* cgroupv2 level to extract */
u8 level_user; /* cgroupv2 level provided by userspace */
u8 len;
union {
u8 dreg;
@ -53,6 +54,28 @@ nft_sock_get_eval_cgroupv2(u32 *dest, struct sock *sk, const struct nft_pktinfo
memcpy(dest, &cgid, sizeof(u64));
return true;
}
/* process context only, uses current->nsproxy. */
static noinline int nft_socket_cgroup_subtree_level(void)
{
struct cgroup *cgrp = cgroup_get_from_path("/");
int level;
if (!cgrp)
return -ENOENT;
level = cgrp->level;
cgroup_put(cgrp);
if (WARN_ON_ONCE(level > 255))
return -ERANGE;
if (WARN_ON_ONCE(level < 0))
return -EINVAL;
return level;
}
#endif
static struct sock *nft_socket_do_lookup(const struct nft_pktinfo *pkt)
@ -174,9 +197,10 @@ static int nft_socket_init(const struct nft_ctx *ctx,
case NFT_SOCKET_MARK:
len = sizeof(u32);
break;
#ifdef CONFIG_CGROUPS
#ifdef CONFIG_SOCK_CGROUP_DATA
case NFT_SOCKET_CGROUPV2: {
unsigned int level;
int err;
if (!tb[NFTA_SOCKET_LEVEL])
return -EINVAL;
@ -185,6 +209,17 @@ static int nft_socket_init(const struct nft_ctx *ctx,
if (level > 255)
return -EOPNOTSUPP;
err = nft_socket_cgroup_subtree_level();
if (err < 0)
return err;
priv->level_user = level;
level += err;
/* Implies a giant cgroup tree */
if (WARN_ON_ONCE(level > 255))
return -EOPNOTSUPP;
priv->level = level;
len = sizeof(u64);
break;
@ -209,7 +244,7 @@ static int nft_socket_dump(struct sk_buff *skb,
if (nft_dump_register(skb, NFTA_SOCKET_DREG, priv->dreg))
return -1;
if (priv->key == NFT_SOCKET_CGROUPV2 &&
nla_put_be32(skb, NFTA_SOCKET_LEVEL, htonl(priv->level)))
nla_put_be32(skb, NFTA_SOCKET_LEVEL, htonl(priv->level_user)))
return -1;
return 0;
}