Mitigate a possible NULL pointer dereference in bpf_get_local_storage() by disallowing tail call to programs that use cgroup storage. Cgroup storage is allocated lazily when attaching a cgroup bpf program. With tail call, it is possible for a callee BPF program to see a NULL storage pointer if the caller prorgam does not use cgroup storage. Reported-by: Yinhao Hu Reported-by: Kaiyan Mei Reported-by: Dongliang Mu Closes: https://lore.kernel.org/bpf/c9ac63d7-73be-49c5-a4ac-eb07f7521adb@hust.edu.cn/ Signed-off-by: Amery Hung --- kernel/bpf/arraymap.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index 1eeb31c5b317..9c3f86ef9d16 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -884,8 +884,9 @@ int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file, void *key, void *value, u64 map_flags) { struct bpf_array *array = container_of(map, struct bpf_array, map); + u32 i, index = *(u32 *)key, ufd; void *new_ptr, *old_ptr; - u32 index = *(u32 *)key, ufd; + struct bpf_prog *prog; if (map_flags != BPF_ANY) return -EINVAL; @@ -898,6 +899,14 @@ int bpf_fd_array_map_update_elem(struct bpf_map *map, struct file *map_file, if (IS_ERR(new_ptr)) return PTR_ERR(new_ptr); + if (map->map_type == BPF_MAP_TYPE_PROG_ARRAY) { + prog = (struct bpf_prog *)new_ptr; + + for_each_cgroup_storage_type(i) + if (prog->aux->cgroup_storage[i]) + return -EINVAL; + } + if (map->ops->map_poke_run) { mutex_lock(&array->aux->poke_mutex); old_ptr = xchg(array->ptrs + index, new_ptr); -- 2.47.3 Check that a BPF program that uses cgroup storage cannot be added to a program array map. Signed-off-by: Amery Hung --- .../selftests/bpf/prog_tests/tailcalls.c | 25 ++++++++++++ .../bpf/progs/tailcall_cgrp_storage.c | 39 +++++++++++++++++++ 2 files changed, 64 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/tailcall_cgrp_storage.c diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c index 0ab36503c3b2..e4a5287f10b1 100644 --- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c +++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c @@ -8,6 +8,7 @@ #include "tailcall_freplace.skel.h" #include "tc_bpf2bpf.skel.h" #include "tailcall_fail.skel.h" +#include "tailcall_cgrp_storage.skel.h" /* test_tailcall_1 checks basic functionality by patching multiple locations * in a single program for a single tail call slot with nop->jmp, jmp->nop @@ -1648,6 +1649,28 @@ static void test_tailcall_bpf2bpf_freplace(void) tc_bpf2bpf__destroy(tc_skel); } +/* + * test_tail_call_cgrp_storage makes sure that callee programs cannot + * use cgroup storage + */ +static void test_tailcall_cgrp_storage(void) +{ + int err, prog_fd, prog_array_fd, key = 0; + struct tailcall_cgrp_storage *skel; + + skel = tailcall_cgrp_storage__open_and_load(); + if (!ASSERT_OK_PTR(skel, "tailcall_cgrp_storage__open_and_load")) + return; + + prog_fd = bpf_program__fd(skel->progs.callee_prog); + prog_array_fd = bpf_map__fd(skel->maps.prog_array); + + err = bpf_map_update_elem(prog_array_fd, &key, &prog_fd, BPF_ANY); + ASSERT_ERR(err, "bpf_map_update_elem"); + + tailcall_cgrp_storage__destroy(skel); +} + static void test_tailcall_failure() { RUN_TESTS(tailcall_fail); @@ -1705,6 +1728,8 @@ void test_tailcalls(void) test_tailcall_freplace(); if (test__start_subtest("tailcall_bpf2bpf_freplace")) test_tailcall_bpf2bpf_freplace(); + if (test__start_subtest("tailcall_cgrp_storage")) + test_tailcall_cgrp_storage(); if (test__start_subtest("tailcall_failure")) test_tailcall_failure(); } diff --git a/tools/testing/selftests/bpf/progs/tailcall_cgrp_storage.c b/tools/testing/selftests/bpf/progs/tailcall_cgrp_storage.c new file mode 100644 index 000000000000..e4f277d2c4fe --- /dev/null +++ b/tools/testing/selftests/bpf/progs/tailcall_cgrp_storage.c @@ -0,0 +1,39 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include + +struct { + __uint(type, BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE); + __type(key, struct bpf_cgroup_storage_key); + __type(value, __u64); +} storage_map SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_PROG_ARRAY); + __uint(max_entries, 1); + __uint(key_size, sizeof(__u32)); + __uint(value_size, sizeof(__u32)); +} prog_array SEC(".maps"); + +SEC("cgroup_skb/egress") +int caller_prog(struct __sk_buff *skb) +{ + bpf_tail_call(skb, &prog_array, 0); + + return 1; +} + +SEC("cgroup_skb/egress") +int callee_prog(struct __sk_buff *skb) +{ + __u64 *storage; + + storage = bpf_get_local_storage(&storage_map, 0); + if (storage) + *storage = 1; + + return 1; +} + +char _license[] SEC("license") = "GPL"; -- 2.47.3