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[178.5.229.20]) by smtp.gmail.com with ESMTPSA id b3-20020aa7d483000000b0054c7dfc63b4sm83786edr.43.2023.12.20.10.08.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Dec 2023 10:08:22 -0800 (PST) From: Dmitrii Dolgov <9erthalion6@gmail.com> To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, dan.carpenter@linaro.org, olsajiri@gmail.com, asavkov@redhat.com, Dmitrii Dolgov <9erthalion6@gmail.com> Subject: [PATCH bpf-next v10 3/4] bpf: Fix re-attachment branch in bpf_tracing_prog_attach Date: Wed, 20 Dec 2023 19:04:18 +0100 Message-ID: <20231220180422.8375-4-9erthalion6@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231220180422.8375-1-9erthalion6@gmail.com> References: <20231220180422.8375-1-9erthalion6@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jiri Olsa The following case can cause a crash due to missing attach_btf: 1) load rawtp program 2) load fentry program with rawtp as target_fd 3) create tracing link for fentry program with target_fd = 0 4) repeat 3 In the end we have: - prog->aux->dst_trampoline == NULL - tgt_prog == NULL (because we did not provide target_fd to link_create) - prog->aux->attach_btf == NULL (the program was loaded with attach_prog_fd=X) - the program was loaded for tgt_prog but we have no way to find out which one BUG: kernel NULL pointer dereference, address: 0000000000000058 Call Trace: ? __die+0x20/0x70 ? page_fault_oops+0x15b/0x430 ? fixup_exception+0x22/0x330 ? exc_page_fault+0x6f/0x170 ? asm_exc_page_fault+0x22/0x30 ? bpf_tracing_prog_attach+0x279/0x560 ? btf_obj_id+0x5/0x10 bpf_tracing_prog_attach+0x439/0x560 __sys_bpf+0x1cf4/0x2de0 __x64_sys_bpf+0x1c/0x30 do_syscall_64+0x41/0xf0 entry_SYSCALL_64_after_hwframe+0x6e/0x76 Return -EINVAL in this situation. Signed-off-by: Jiri Olsa Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com> --- kernel/bpf/syscall.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index c40cad8886e9..5096ddfbe426 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3201,6 +3201,10 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, * * - if prog->aux->dst_trampoline and tgt_prog is NULL, the program * was detached and is going for re-attachment. + * + * - if prog->aux->dst_trampoline is NULL and tgt_prog and prog->aux->attach_btf + * are NULL, then program was already attached and user did not provide + * tgt_prog_fd so we have no way to find out or create trampoline */ if (!prog->aux->dst_trampoline && !tgt_prog) { /* @@ -3214,6 +3218,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, err = -EINVAL; goto out_unlock; } + /* We can allow re-attach only if we have valid attach_btf. */ + if (!prog->aux->attach_btf) { + err = -EINVAL; + goto out_unlock; + } btf_id = prog->aux->attach_btf_id; key = bpf_trampoline_compute_key(NULL, prog->aux->attach_btf, btf_id); } -- 2.41.0