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Message-ID: <20240819181825.18235-1-kuniyu@amazon.com>
Date: Mon, 19 Aug 2024 11:18:25 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <tze-nan.wu@...iatek.com>
CC: <angelogioacchino.delregno@...labora.com>, <bobule.chang@...iatek.com>,
<cheng-jui.wang@...iatek.com>, <davem@...emloft.net>, <edumazet@...gle.com>,
<kuba@...nel.org>, <linux-kernel@...r.kernel.org>,
<linux-mediatek@...ts.infradead.org>, <matthias.bgg@...il.com>,
<netdev@...r.kernel.org>, <pabeni@...hat.com>, <sdf@...ichev.me>,
<wsd_upstream@...iatek.com>, <yanghui.li@...iatek.com>, <kuniyu@...zon.com>
Subject: Re: [PATCH v2] net/socket: Check cgroup_bpf_enabled() only once in do_sock_getsockopt
From: Tze-nan Wu <Tze-nan.Wu@...iatek.com>
Date: Mon, 19 Aug 2024 23:56:27 +0800
> The return value from `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` can change
> between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
> `BPF_CGROUP_RUN_PROG_GETSOCKOPT`.
>
> If `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` changes from "false" to
> "true" between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
> `BPF_CGROUP_RUN_PROG_GETSOCKOPT`, `BPF_CGROUP_RUN_PROG_GETSOCKOPT` will
> receive an -EFAULT from `__cgroup_bpf_run_filter_getsockopt(max_optlen=0)`
> due to `get_user()` was not reached in `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN`.
>
> Scenario shown as below:
>
> `process A` `process B`
> ----------- ------------
> BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN
> enable CGROUP_GETSOCKOPT
> BPF_CGROUP_RUN_PROG_GETSOCKOPT (-EFAULT)
>
> To prevent this, invoke `cgroup_bpf_enabled()` only once and cache the
> result in a newly added local variable `enabled`.
> Both `BPF_CGROUP_*` macros in `do_sock_getsockopt` will then check their
> condition using the same `enabled` variable as the condition variable,
> instead of using the return values from `cgroup_bpf_enabled` called by
> themselves as the condition variable(which could yield different results).
> This ensures that either both `BPF_CGROUP_*` macros pass the condition
> or neither does.
>
> Co-developed-by: Yanghui Li <yanghui.li@...iatek.com>
> Signed-off-by: Yanghui Li <yanghui.li@...iatek.com>
> Co-developed-by: Cheng-Jui Wang <cheng-jui.wang@...iatek.com>
> Signed-off-by: Cheng-Jui Wang <cheng-jui.wang@...iatek.com>
> Signed-off-by: Tze-nan Wu <Tze-nan.Wu@...iatek.com>
> ---
>
> Chagnes from v1 to v2: https://lore.kernel.org/all/20240819082513.27176-1-Tze-nan.Wu@mediatek.com/
> Instead of using cgroup_lock in the fastpath, invoke cgroup_bpf_enabled
> only once and cache the value in the variable `enabled`. `BPF_CGROUP_*`
> macros in do_sock_getsockopt can then both check their condition with
> the same variable, ensuring that either they both passing the condition
> or both do not.
>
> Appreciate for reviewing this!
> This patch should make cgroup_bpf_enabled() only using once,
> but not sure if "BPF_CGROUP_*" is modifiable?(not familiar with code here)
>
> If it's not, then maybe I can come up another patch like below one:
> +++ b/net/socket.c
> int max_optlen __maybe_unused;
> const struct proto_ops *ops;
> int err;
> + bool enabled;
>
> err = security_socket_getsockopt(sock, level, optname);
> if (err)
> return err;
>
> - if (!compat)
> + enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);
> + if (!compat && enabled)
> max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
>
> But this will cause do_sock_getsockopt calling cgroup_bpf_enabled up to
> three times , Wondering which approach will be more acceptable?
>
> ---
> include/linux/bpf-cgroup.h | 13 ++++++-------
> net/socket.c | 9 ++++++---
> 2 files changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> index fb3c3e7181e6..251632d52fa9 100644
> --- a/include/linux/bpf-cgroup.h
> +++ b/include/linux/bpf-cgroup.h
> @@ -390,20 +390,19 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
> __ret; \
> })
>
> -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) \
> +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled) \
Please keep \ aligned. Same for other places.
> ({ \
> int __ret = 0; \
> - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT)) \
Can you assign 'enabled' here to hide its usage in the macro ?
> + if (enabled) \
> copy_from_sockptr(&__ret, optlen, sizeof(int)); \
> __ret; \
> })
>
> #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname, optval, optlen, \
> - max_optlen, retval) \
> + max_optlen, retval, enabled) \
> ({ \
> int __ret = retval; \
> - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT) && \
> - cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT)) \
> + if (enabled && cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT)) \
> if (!(sock)->sk_prot->bpf_bypass_getsockopt || \
> !INDIRECT_CALL_INET_1((sock)->sk_prot->bpf_bypass_getsockopt, \
> tcp_bpf_bypass_getsockopt, \
> @@ -518,9 +517,9 @@ static inline int bpf_percpu_cgroup_storage_update(struct bpf_map *map,
> #define BPF_CGROUP_RUN_PROG_SOCK_OPS(sock_ops) ({ 0; })
> #define BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(atype, major, minor, access) ({ 0; })
> #define BPF_CGROUP_RUN_PROG_SYSCTL(head,table,write,buf,count,pos) ({ 0; })
> -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) ({ 0; })
> +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled) ({ 0; })
> #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname, optval, \
> - optlen, max_optlen, retval) ({ retval; })
> + optlen, max_optlen, retval, enabled) ({ retval; })
> #define BPF_CGROUP_RUN_PROG_GETSOCKOPT_KERN(sock, level, optname, optval, \
> optlen, retval) ({ retval; })
> #define BPF_CGROUP_RUN_PROG_SETSOCKOPT(sock, level, optname, optval, optlen, \
> diff --git a/net/socket.c b/net/socket.c
> index fcbdd5bc47ac..5336a2755bb4 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2365,13 +2365,16 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
> int max_optlen __maybe_unused;
> const struct proto_ops *ops;
> int err;
> + bool enabled;
Please keep reverse xmas tree order.
https://docs.kernel.org/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs
>
> err = security_socket_getsockopt(sock, level, optname);
> if (err)
> return err;
>
> - if (!compat)
> - max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> + if (!compat) {
> + enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);
> + max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled);
> + }
>
> ops = READ_ONCE(sock->ops);
> if (level == SOL_SOCKET) {
> @@ -2390,7 +2393,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
> if (!compat)
> err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level, optname,
> optval, optlen, max_optlen,
> - err);
> + err, enabled);
>
> return err;
> }
> --
> 2.45.2
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