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([2620:10d:c092:500::6:7242]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-495516c68fasm207736295e9.1.2026.07.20.07.16.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jul 2026 07:16:21 -0700 (PDT) Message-ID: <1289e62e-e956-40c9-a93b-22feefb9110f@gmail.com> Date: Mon, 20 Jul 2026 15:16:18 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf v4 3/4] bpf: Fix potential UAF when reading bpf link info To: Pu Lehui , bpf@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Yonghong Song , Song Liu , Jiri Olsa , Emil Tsalapatis , Pu Lehui References: <20260720134547.1289964-1-pulehui@huaweicloud.com> <20260720134547.1289964-4-pulehui@huaweicloud.com> Content-Language: en-US From: Mykyta Yatsenko In-Reply-To: <20260720134547.1289964-4-pulehui@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/20/26 2:45 PM, Pu Lehui wrote: > From: Pu Lehui > > In bpf_link_show_fdinfo and bpf_link_get_info_by_fd, link->prog is > accessed without holding any locks. If the prog is concurrently replaced > via bpf_link_update, the old prog can be freed, leading to a potential > UAF issue. > > Fix this by holding both normal RCU and tasks trace RCU read locks > before dereferencing the prog, as BPF_LINK_TYPE_ITER support both > non-sleepable and sleepable progs. > > Fixes: 0c991ebc8c69 ("bpf: Implement bpf_prog replacement for an active bpf_cgroup_link") > Reported-by: Sashiko > Signed-off-by: Pu Lehui > --- > kernel/bpf/syscall.c | 27 +++++++++++++++++++++++---- > 1 file changed, 23 insertions(+), 4 deletions(-) > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 6db306d23b47..2458c68146b9 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -3471,9 +3471,10 @@ static const char *bpf_link_type_strs[] = { > static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp) > { > const struct bpf_link *link = filp->private_data; > - const struct bpf_prog *prog = link->prog; > + const struct bpf_prog *prog; > enum bpf_link_type type = link->type; > char prog_tag[sizeof(prog->tag) * 2 + 1] = { }; > + u32 prog_id; > > if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) { > if (link->type == BPF_LINK_TYPE_KPROBE_MULTI) > @@ -3490,13 +3491,23 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp) > } > seq_printf(m, "link_id:\t%u\n", link->id); > > + /* prog can be sleepable */ > + rcu_read_lock_trace(); > + rcu_read_lock(); Only rcu_read_lock() should be enough, see 57b23c0f612d ("bpf: Retire rcu_trace_implies_rcu_gp()") Did you manage to reproduce the UAF? > + prog = READ_ONCE(link->prog); > if (prog) { > bin2hex(prog_tag, prog->tag, sizeof(prog->tag)); > + prog_id = prog->aux->id; > + } > + rcu_read_unlock(); > + rcu_read_unlock_trace(); > + > + if (prog) { > seq_printf(m, > "prog_tag:\t%s\n" > "prog_id:\t%u\n", > prog_tag, > - prog->aux->id); > + prog_id); > } > if (link->ops->show_fdinfo) > link->ops->show_fdinfo(link, m); > @@ -5535,6 +5546,7 @@ static int bpf_link_get_info_by_fd(struct file *file, > { > struct bpf_link_info __user *uinfo = u64_to_user_ptr(attr->info.info); > struct bpf_link_info info; > + const struct bpf_prog *prog; > u32 info_len = attr->info.info_len; > int err; > > @@ -5549,8 +5561,15 @@ static int bpf_link_get_info_by_fd(struct file *file, > > info.type = link->type; > info.id = link->id; > - if (link->prog) > - info.prog_id = link->prog->aux->id; > + > + /* prog can be sleepable */ > + rcu_read_lock_trace(); > + rcu_read_lock(); > + prog = READ_ONCE(link->prog); > + if (prog) > + info.prog_id = prog->aux->id; > + rcu_read_unlock(); > + rcu_read_unlock_trace(); > > if (link->ops->fill_link_info) { > err = link->ops->fill_link_info(link, &info);