Since there're 4 bytes padding at the end of struct bpf_map_info, they won't be checked by bpf_check_uarg_tail_zero(). pahole -C bpf_map_info ./vmlinux struct bpf_map_info { ... __u64 hash __attribute__((__aligned__(8))); /* 88 8 */ __u32 hash_size; /* 96 4 */ /* size: 104, cachelines: 2, members: 18 */ /* padding: 4 */ /* forced alignments: 1 */ /* last cacheline: 40 bytes */ } __attribute__((__aligned__(8))); If a future kernel extension adds a new 4-byte field, older userspace programs allocating this structure on the stack might inadvertently pass uninitialized stack garbage into the new field, permanently breaking backward compatibility. -- sashiko [1] Fix it by changing sizeof(info) to offsetofend(struct bpf_map_info, hash_size). And, add "__u32 :32" to the tail of struct bpf_map_info. [1] https://lore.kernel.org/bpf/20260513224823.6494FC19425@smtp.kernel.org/ Fixes: ea2e6467ac36 ("bpf: Return hashes of maps in BPF_OBJ_GET_INFO_BY_FD") Acked-by: Mykyta Yatsenko Signed-off-by: Leon Hwang --- include/uapi/linux/bpf.h | 1 + kernel/bpf/syscall.c | 5 +++-- tools/include/uapi/linux/bpf.h | 1 + 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index bed9b1b4d5ef..e1730f449d9e 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -6733,6 +6733,7 @@ struct bpf_map_info { __u64 map_extra; __aligned_u64 hash; __u32 hash_size; + __u32 :32; } __attribute__((aligned(8))); struct bpf_btf_info { diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 31a3b70a0b5d..89f020a44fc9 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -5406,10 +5406,11 @@ static int bpf_map_get_info_by_fd(struct file *file, { struct bpf_map_info __user *uinfo = u64_to_user_ptr(attr->info.info); struct bpf_map_info info; - u32 info_len = attr->info.info_len; + u32 info_len = attr->info.info_len, len; int err; - err = bpf_check_uarg_tail_zero(USER_BPFPTR(uinfo), sizeof(info), info_len); + len = offsetofend(struct bpf_map_info, hash_size); + err = bpf_check_uarg_tail_zero(USER_BPFPTR(uinfo), len, info_len); if (err) return err; info_len = min_t(u32, sizeof(info), info_len); diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 7d0b282ba674..7caf667e86fe 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -6733,6 +6733,7 @@ struct bpf_map_info { __u64 map_extra; __aligned_u64 hash; __u32 hash_size; + __u32 :32; } __attribute__((aligned(8))); struct bpf_btf_info { -- 2.54.0 Since there're 4 bytes padding at the end of struct bpf_prog_info, they won't be checked by bpf_check_uarg_tail_zero(). pahole -C bpf_prog_info ./vmlinux struct bpf_prog_info { ... __u32 attach_btf_obj_id; /* 220 4 */ __u32 attach_btf_id; /* 224 4 */ /* size: 232, cachelines: 4, members: 38 */ /* sum members: 224 */ /* sum bitfield members: 1 bits, bit holes: 1, sum bit holes: 31 bits */ /* padding: 4 */ /* forced alignments: 9 */ /* last cacheline: 40 bytes */ } __attribute__((__aligned__(8))); If a future kernel extension adds a new 4-byte field, older userspace programs allocating this structure on the stack might inadvertently pass uninitialized stack garbage into the new field, permanently breaking backward compatibility. -- sashiko [1] Fix it by changing sizeof(info) to offsetofend(struct bpf_prog_info, attach_btf_id). And, add "__u32 :32" to the tail of struct bpf_prog_info. [1] https://lore.kernel.org/bpf/20260513224823.6494FC19425@smtp.kernel.org/ Fixes: aba64c7da983 ("bpf: Add verified_insns to bpf_prog_info and fdinfo") Acked-by: Mykyta Yatsenko Signed-off-by: Leon Hwang --- include/uapi/linux/bpf.h | 1 + kernel/bpf/syscall.c | 5 +++-- tools/include/uapi/linux/bpf.h | 1 + 3 files changed, 5 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index e1730f449d9e..d5238df5e5eb 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -6712,6 +6712,7 @@ struct bpf_prog_info { __u32 verified_insns; __u32 attach_btf_obj_id; __u32 attach_btf_id; + __u32 :32; } __attribute__((aligned(8))); struct bpf_map_info { diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 89f020a44fc9..c5d4ae957e87 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -5121,10 +5121,11 @@ static int bpf_prog_get_info_by_fd(struct file *file, u32 info_len = attr->info.info_len; struct bpf_prog_kstats stats; char __user *uinsns; - u32 ulen; + u32 ulen, len; int err; - err = bpf_check_uarg_tail_zero(USER_BPFPTR(uinfo), sizeof(info), info_len); + len = offsetofend(struct bpf_prog_info, attach_btf_id); + err = bpf_check_uarg_tail_zero(USER_BPFPTR(uinfo), len, info_len); if (err) return err; info_len = min_t(u32, sizeof(info), info_len); diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 7caf667e86fe..3829db087449 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -6712,6 +6712,7 @@ struct bpf_prog_info { __u32 verified_insns; __u32 attach_btf_obj_id; __u32 attach_btf_id; + __u32 :32; } __attribute__((aligned(8))); struct bpf_map_info { -- 2.54.0 Add two tests to verify that the tail padding 4 bytes of struct bpf_map_info and bpf_prog_info are checked in syscall.c using bpf_check_uarg_tail_zero(). Signed-off-by: Leon Hwang --- .../selftests/bpf/prog_tests/bpf_attr_size.c | 55 +++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_attr_size.c b/tools/testing/selftests/bpf/prog_tests/bpf_attr_size.c index 32159dc64da8..87842c4347a6 100644 --- a/tools/testing/selftests/bpf/prog_tests/bpf_attr_size.c +++ b/tools/testing/selftests/bpf/prog_tests/bpf_attr_size.c @@ -62,8 +62,63 @@ static void test_query_size_boundaries(void) cgroup_skb_direct_packet_access__destroy(skel); } +static void test_map_info_tail_zero(void) +{ + LIBBPF_OPTS(bpf_map_create_opts, map_opts); + struct bpf_map_info_fake { + __u8 info[offsetofend(struct bpf_map_info, hash_size)]; + __u32 pad; + } info = { + .pad = 1, + }; + int map_fd, err; + __u32 info_len; + + map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "arr", sizeof(int), 1, 1, &map_opts); + if (!ASSERT_GE(map_fd, 0, "bpf_map_create")) + return; + + info_len = sizeof(info); + err = bpf_obj_get_info_by_fd(map_fd, &info, &info_len); + ASSERT_EQ(err, -E2BIG, "bpf_obj_get_info_by_fd"); + + close(map_fd); +} + +static void test_prog_info_tail_zero(void) +{ + LIBBPF_OPTS(bpf_prog_load_opts, prog_opts); + struct bpf_insn insns[] = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }; + struct bpf_prog_info_fake { + __u8 info[offsetofend(struct bpf_prog_info, attach_btf_id)]; + __u32 pad; + } info = { + .pad = 1, + }; + int prog_fd, err; + __u32 info_len; + + prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "test_prog", "GPL", insns, + ARRAY_SIZE(insns), &prog_opts); + if (!ASSERT_GE(prog_fd, 0, "bpf_prog_load")) + return; + + info_len = sizeof(info); + err = bpf_obj_get_info_by_fd(prog_fd, &info, &info_len); + ASSERT_EQ(err, -E2BIG, "bpf_obj_get_info_by_fd"); + + close(prog_fd); +} + void test_bpf_attr_size(void) { if (test__start_subtest("query_size_boundaries")) test_query_size_boundaries(); + if (test__start_subtest("map_info_tail_zero")) + test_map_info_tail_zero(); + if (test__start_subtest("prog_info_tail_zero")) + test_prog_info_tail_zero(); } -- 2.54.0