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Sun, 30 Aug 2026 19:39:32 -0700 (PDT) From: Sanghyun Park To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , bpf@vger.kernel.org Cc: Sanghyun Park , Leon Hwang , John Fastabend , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Shuah Khan , Stanislav Fomichev , Pu Lehui , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf-next v4 1/2] bpf: Validate program attach type during link update Date: Mon, 31 Aug 2026 11:39:11 +0900 Message-ID: <20260831023918.1857658-1-sanghyun.park.cnu@gmail.com> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Cgroup link updates compare only the program type. Programs verified for different hooks can share a type, so a UDP6 sock_addr program can replace a UDP4 program and write beyond the four-byte ipc.addr field in the stack-local struct ipcm_cookie. The same gap permits incompatible LSM_MAC and LSM_CGROUP replacements. Validate every replacement program against the link attach type before dispatching to the link-specific update operation. Keep the CGROUP_SKB CAP_NET_ADMIN check at initial attach so pinned or delegated link FDs can still be updated after a capability drop. Fixes: 0c991ebc8c69 ("bpf: Implement bpf_prog replacement for an active bpf_cgroup_link") Signed-off-by: Sanghyun Park --- v4: - Validate every program link update through the shared attach-type helper. - Fold the LSM attach-flavor check into that helper. - Keep the CGROUP_SKB permission check in the attach-only wrapper and rename the wrapper to describe that role. - Follow the preferred BPF multi-line comment style. - Add focused regression selftests as patch 2/2. v3: https://lore.kernel.org/r/20260821084726.3769957-2-sanghyun.park.cnu@gmail.com - Factor the CGROUP_SKB CAP_NET_ADMIN check into an attach-only helper. v2: https://lore.kernel.org/r/20260818061021.2551771-2-sanghyun.park.cnu@gmail.com - Extend validation from cgroup sock_addr programs to all cgroup program types, including exact LSM attach flavors. - Preserve legacy CGROUP_SKB ingress/egress replacement compatibility. - Keep the CGROUP_SKB CAP_NET_ADMIN check on attach, not link update. v1: https://lore.kernel.org/r/20260805052858.2390918-3-sanghyun.park.cnu@gmail.com --- kernel/bpf/syscall.c | 31 ++++++++++++++++++++++--------- 1 file changed, 22 insertions(+), 9 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 6874ba1424af..84823149dffa 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -4481,14 +4481,9 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog, case BPF_PROG_TYPE_CGROUP_SOCK_ADDR: case BPF_PROG_TYPE_CGROUP_SOCKOPT: case BPF_PROG_TYPE_SK_LOOKUP: + case BPF_PROG_TYPE_LSM: return attach_type == prog->expected_attach_type ? 0 : -EINVAL; case BPF_PROG_TYPE_CGROUP_SKB: - if (!bpf_token_capable(prog->aux->token, CAP_NET_ADMIN)) - /* cg-skb progs can be loaded by unpriv user. - * check permissions at attach time. - */ - return -EPERM; - ptype = attach_type_to_prog_type(attach_type); if (prog->type != ptype) return -EINVAL; @@ -4542,6 +4537,20 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog, } } +static int bpf_prog_attach_check_perm(const struct bpf_prog *prog, + enum bpf_attach_type attach_type) +{ + /* + * CGROUP_SKB programs can be loaded by unprivileged users, so check + * permissions at attach time. + */ + if (prog->type == BPF_PROG_TYPE_CGROUP_SKB && + !bpf_token_capable(prog->aux->token, CAP_NET_ADMIN)) + return -EPERM; + + return bpf_prog_attach_check_attach_type(prog, attach_type); +} + static bool is_cgroup_prog_type(enum bpf_prog_type ptype, enum bpf_attach_type atype, bool check_atype) { @@ -4606,7 +4615,7 @@ static int bpf_prog_attach(const union bpf_attr *attr) if (IS_ERR(prog)) return PTR_ERR(prog); - if (bpf_prog_attach_check_attach_type(prog, attr->attach_type)) { + if (bpf_prog_attach_check_perm(prog, attr->attach_type)) { bpf_prog_put(prog); return -EINVAL; } @@ -5805,8 +5814,8 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) if (IS_ERR(prog)) return PTR_ERR(prog); - ret = bpf_prog_attach_check_attach_type(prog, - attr->link_create.attach_type); + ret = bpf_prog_attach_check_perm(prog, + attr->link_create.attach_type); if (ret) goto out; @@ -5968,6 +5977,10 @@ static int link_update(union bpf_attr *attr) goto out_put_progs; } + ret = bpf_prog_attach_check_attach_type(new_prog, link->attach_type); + if (ret) + goto out_put_progs; + if (link->ops->update_prog) ret = link->ops->update_prog(link, new_prog, old_prog); else -- 2.48.1