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Tue, 27 Jan 2026 00:26:57 -0800 (PST) From: Guillaume Gonnet To: alexei.starovoitov@gmail.com Cc: ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, ggonnet.linux@gmail.com, john.fastabend@gmail.com, martin.lau@linux.dev Subject: [PATCH bpf v4] bpf: Fix tcx/netkit detach permissions when prog fd isn't given Date: Tue, 27 Jan 2026 09:26:16 +0100 Message-Id: <20260127082616.28850-1-ggonnet.linux@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This commit fixes a security issue where BPF_PROG_DETACH on tcx or netkit devices could be executed by any user when no program fd was provided, bypassing permission checks. The fix adds a capability check for CAP_NET_ADMIN or CAP_SYS_ADMIN in this case. Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support") Signed-off-by: Guillaume Gonnet --- include/linux/bpf.h | 5 +++++ include/linux/bpf_mprog.h | 12 ++++++++++++ kernel/bpf/syscall.c | 7 ++----- 3 files changed, 19 insertions(+), 5 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 4427c6e98331..5f59d1f173a2 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2742,6 +2742,11 @@ static inline bool bpf_bypass_spec_v4(const struct bpf_token *token) bpf_token_capable(token, CAP_PERFMON); } +static inline bool bpf_net_capable(void) +{ + return capable(CAP_NET_ADMIN) || capable(CAP_SYS_ADMIN); +} + int bpf_map_new_fd(struct bpf_map *map, int flags); int bpf_prog_new_fd(struct bpf_prog *prog); diff --git a/include/linux/bpf_mprog.h b/include/linux/bpf_mprog.h index 929225f7b095..18d26ae6a5b6 100644 --- a/include/linux/bpf_mprog.h +++ b/include/linux/bpf_mprog.h @@ -340,4 +340,16 @@ static inline bool bpf_mprog_supported(enum bpf_prog_type type) return false; } } + +#ifdef CONFIG_BPF_SYSCALL +static inline bool bpf_mprog_detach_empty(enum bpf_prog_type type) +{ + switch (type) { + case BPF_PROG_TYPE_SCHED_CLS: + return bpf_net_capable(); + default: + return false; + } +} +#endif /* CONFIG_BPF_SYSCALL */ #endif /* __BPF_MPROG_H */ diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index b9184545c3fd..5f59dd47a5b1 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1363,11 +1363,6 @@ static int map_check_btf(struct bpf_map *map, struct bpf_token *token, return ret; } -static bool bpf_net_capable(void) -{ - return capable(CAP_NET_ADMIN) || capable(CAP_SYS_ADMIN); -} - #define BPF_MAP_CREATE_LAST_FIELD excl_prog_hash_size /* called via syscall */ static int map_create(union bpf_attr *attr, bpfptr_t uattr) @@ -4579,6 +4574,8 @@ static int bpf_prog_detach(const union bpf_attr *attr) prog = bpf_prog_get_type(attr->attach_bpf_fd, ptype); if (IS_ERR(prog)) return PTR_ERR(prog); + } else if (!bpf_mprog_detach_empty(ptype)) { + return -EPERM; } } else if (is_cgroup_prog_type(ptype, 0, false)) { if (attr->attach_flags || attr->relative_fd) -- 2.34.1