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[69.172.153.146]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a06cb7159fsm1774824a91.4.2026.09.22.10.20.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 10:20:49 -0700 (PDT) From: Emil Tsalapatis To: bpf@vger.kernel.org Cc: ast@kernel.org, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, daniel@iogearbox.net, netdev@vger.kernel.org, Emil Tsalapatis Subject: [PATCH bpf v2 11/11] selftests/bpf: Test dynptr slice invalidation on skb clobber Date: Tue, 22 Sep 2026 17:20:28 +0000 Message-ID: <20260922172028.6269-12-emil@etsalapatis.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260922172028.6269-1-emil@etsalapatis.com> References: <20260922172028.6269-1-emil@etsalapatis.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add tests that ensure that dynptr slices backed by skb memory are invalidated on any operation that potentially moves/frees the backing skb memory. Also test that only skb-backed dynptrs may invalidate pointers into skbs. Signed-off-by: Emil Tsalapatis --- .../testing/selftests/bpf/progs/dynptr_fail.c | 183 ++++++++++++++++++ 1 file changed, 183 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c index 1cd61d72c..0f030f397 100644 --- a/tools/testing/selftests/bpf/progs/dynptr_fail.c +++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c @@ -13,6 +13,9 @@ char _license[] SEC("license") = "GPL"; +extern int bpf_dynptr_memset(const struct bpf_dynptr *p, __u64 offset, __u64 size, + __u8 val) __ksym __weak; + struct test_info { int x; struct bpf_dynptr ptr; @@ -1274,6 +1277,186 @@ int skb_invalid_data_slice4(struct __sk_buff *skb) return SK_PASS; } +/* + * A kfunc that may clobber packet pointers must invalidate skb data slices. + */ +SEC("?tc") +__failure __msg("invalid mem access") +int skb_invalid_data_slice_after_dynptr_memset(struct __sk_buff *skb) +{ + struct bpf_dynptr ptr; + struct ethhdr *hdr; + char buffer[sizeof(*hdr)] = {}; + + bpf_dynptr_from_skb(skb, 0, &ptr); + + hdr = bpf_dynptr_slice_rdwr(&ptr, 0, buffer, sizeof(buffer)); + if (!hdr) + return SK_DROP; + + bpf_dynptr_memset(&ptr, 0, 0, 0); + + /* this should fail */ + val = hdr->h_proto; + + return SK_PASS; +} + +/* + * A dynptr kfunc that may clobber packet pointers must not invalidate packet + * pointers when called with a non-skb dynptr. + */ +SEC("?tc") +__success +int pkt_ptr_valid_after_dynptr_memset_on_mem(struct __sk_buff *skb) +{ + struct bpf_dynptr ptr; + int *p = (void *)(long)skb->data; + + if ((void *)(p + 1) > (void *)(long)skb->data_end) + return SK_DROP; + + if (bpf_dynptr_from_mem(&val, sizeof(val), 0, &ptr)) + return SK_DROP; + + bpf_dynptr_memset(&ptr, 0, 0, 0); + + return *p ? SK_PASS : SK_DROP; +} + +__noinline +int skb_dynptr_memset(struct __sk_buff *skb) +{ + struct bpf_dynptr ptr; + + if (bpf_dynptr_from_skb(skb, 0, &ptr)) + return 0; + + return bpf_dynptr_memset(&ptr, 0, 0, 0); +} + +/* + * A global subprog that may clobber packet pointers must invalidate packet + * pointers held by its caller. + */ +SEC("?tc") +__failure __msg("invalid mem access") +int skb_invalid_pkt_ptr_after_dynptr_memset_global(struct __sk_buff *skb) +{ + int *p = (void *)(long)skb->data; + + if ((void *)(p + 1) > (void *)(long)skb->data_end) + return SK_DROP; + + skb_dynptr_memset(skb); + + /* this should fail */ + val = *p; + + return SK_PASS; +} + +__noinline +int skb_dynptr_memset_global_arg(struct __sk_buff *skb, + struct bpf_dynptr *ptr) +{ + int *p = (void *)(long)skb->data; + + if ((void *)(p + 1) > (void *)(long)skb->data_end) + return SK_DROP; + + bpf_dynptr_memset(ptr, 0, sizeof(*p), 0); + + /* this should fail */ + val = *p; + + return SK_PASS; +} + +/* + * A global subprog must conservatively treat a dynptr argument as possibly + * skb-backed when checking whether a kfunc invalidates packet pointers. + */ +SEC("?tc") +__failure __msg("invalid mem access") +int skb_invalid_pkt_ptr_after_dynptr_memset_global_arg(struct __sk_buff *skb) +{ + struct bpf_dynptr ptr; + + if (bpf_dynptr_from_skb(skb, 0, &ptr)) + return SK_DROP; + + return skb_dynptr_memset_global_arg(skb, &ptr); +} + +__noinline +int skb_dynptr_write_global_arg(struct bpf_dynptr *ptr) +{ + int write_data = 0; + + return bpf_dynptr_write(ptr, 0, &write_data, sizeof(write_data), 0); +} + +/* + * A global subprog that calls bpf_dynptr_write() on a dynptr argument must + * invalidate packet pointers held by its caller. + */ +SEC("?tc") +__failure __msg("invalid mem access") +int skb_invalid_pkt_ptr_after_dynptr_write_global_arg(struct __sk_buff *skb) +{ + struct bpf_dynptr ptr; + int *p = (void *)(long)skb->data; + + if ((void *)(p + 1) > (void *)(long)skb->data_end) + return SK_DROP; + + if (bpf_dynptr_from_skb(skb, 0, &ptr)) + return SK_DROP; + + skb_dynptr_write_global_arg(&ptr); + + /* this should fail */ + val = *p; + + return SK_PASS; +} + +__noinline +int skb_dynptr_write_global_arg_with_pkt_ptr(struct __sk_buff *skb, + struct bpf_dynptr *ptr) +{ + int write_data = 0; + int *p = (void *)(long)skb->data; + + if ((void *)(p + 1) > (void *)(long)skb->data_end) + return SK_DROP; + + bpf_dynptr_write(ptr, 0, &write_data, sizeof(write_data), 0); + + /* this should fail */ + val = *p; + + return SK_PASS; +} + +/* + * A global subprog must conservatively treat a dynptr argument as possibly + * skb-backed when checking whether bpf_dynptr_write() invalidates packet + * pointers in the callee. + */ +SEC("?tc") +__failure __msg("invalid mem access") +int skb_invalid_pkt_ptr_after_dynptr_write_global_arg_in_subprog(struct __sk_buff *skb) +{ + struct bpf_dynptr ptr; + + if (bpf_dynptr_from_skb(skb, 0, &ptr)) + return SK_DROP; + + return skb_dynptr_write_global_arg_with_pkt_ptr(skb, &ptr); +} + /* Read-only skb data slice is invalidated on write to skb metadata */ SEC("?tc") __failure __msg("invalid mem access 'scalar'") -- 2.54.0