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Message-ID: <b8348f42ef7e78e391619b198ee9a92eb74524e8.camel@mediatek.com>
Date: Thu, 22 Aug 2024 03:28:00 +0000
From: Tze-nan Wu (吳澤南) <Tze-nan.Wu@...iatek.com>
To: "yonghong.song@...ux.dev" <yonghong.song@...ux.dev>
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<matthias.bgg@...il.com>
Subject: Re: [PATCH net v4] bpf, net: Check cgroup_bpf_enabled() only once in
do_sock_getsockopt()
On Wed, 2024-08-21 at 11:44 -0700, Yonghong Song wrote:
>
>
> On 8/21/24 2:30 AM, Tze-nan Wu wrote:
> > 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.
> >
> > Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt
> hooks")
> > 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 newly added variable
> `enabled`.
> > `BPF_CGROUP_*` macros in do_sock_getsockopt can then both check
> their
> > condition with the new variable `enable`, ensuring that either
> they both
> > passing the condition or both do not.
> >
> > Chagnes from v2 to v3:
> https://lore.kernel.org/all/20240819155627.1367-1-Tze-nan.Wu@mediatek.com/
> > Hide cgroup_bpf_enabled in the macro, and some modifications to
> adapt
> > the coding style.
> >
> > Chagnes from v3 to v4:
> https://lore.kernel.org/all/20240820092942.16654-1-Tze-nan.Wu@mediatek.com/
> > Add bpf tag to subject, and Fixes tag in body.
> >
> > ---
> > include/linux/bpf-cgroup.h | 15 ++++++++-------
> > net/socket.c | 5 +++--
> > 2 files changed, 11 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-
> cgroup.h
> > index fb3c3e7181e6..5afa2ac76aae 100644
> > --- a/include/linux/bpf-cgroup.h
> > +++ b/include/linux/bpf-cgroup.h
> > @@ -390,20 +390,20 @@ 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) \
> > ({ \
> > int __ret = 0; \
> > -if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT)) \
> > +enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT); \
> > +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 +518,10 @@ 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..0b465dc8a789 100644
> > --- a/net/socket.c
> > +++ b/net/socket.c
> > @@ -2363,6 +2363,7 @@ int do_sock_getsockopt(struct socket *sock,
> bool compat, int level,
> > int optname, sockptr_t optval, sockptr_t optlen)
> > {
> > int max_optlen __maybe_unused;
> > +bool enabled __maybe_unused;
> > const struct proto_ops *ops;
> > int err;
> >
> > @@ -2371,7 +2372,7 @@ int do_sock_getsockopt(struct socket *sock,
> bool compat, int level,
> > return err;
> >
> > if (!compat)
> > -max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> > +max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled);
>
> Here, 'enabled' is actually assigned with a value in the macro. I am
> not sure
> whether this is a common practice or not. At least from macro, it is
> not clear
> about this.
>
> Maybe we can do
> max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, &enabled);
>
> The &enabled signals that its value could change. And indeed
> the macro will store the proper value to &enabled properly.
>
> Just my 2 cents.
>
Thanks for the suggestion.
Will take the suggestion in v5 if this patch is truely needed,
looks like this patch could possibly lead to regression issue.
> >
> > ops = READ_ONCE(sock->ops);
> > if (level == SOL_SOCKET) {
> > @@ -2390,7 +2391,7 @@ 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;
> > }
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