Syzkaller found a kernel warning on the following sock_addr program: 0: r0 = 0 1: r2 = *(u32 *)(r1 +60) 2: exit which triggers: verifier bug: error during ctx access conversion (0) This is happening because offset 60 in bpf_sock_addr corresponds to an implicit padding of 4 bytes, right after msg_src_ip4. Access to this padding isn't rejected in sock_addr_is_valid_access and it thus later fails to convert the access. This patch fixes it by explicitly checking the various fields of bpf_sock_addr in sock_addr_is_valid_access. I checked the other ctx structures and is_valid_access functions and didn't find any other similar cases. Other cases of (properly handled) padding are covered in new tests in a subsequent patch. Fixes: 1cedee13d25a ("bpf: Hooks for sys_sendmsg") Reported-by: syzbot+136ca59d411f92e821b7@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=136ca59d411f92e821b7 Acked-by: Eduard Zingerman Signed-off-by: Paul Chaignon --- net/core/filter.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/net/core/filter.c b/net/core/filter.c index 63f3baee2daf..8342f810ad85 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -9284,13 +9284,17 @@ static bool sock_addr_is_valid_access(int off, int size, return false; info->reg_type = PTR_TO_SOCKET; break; - default: - if (type == BPF_READ) { - if (size != size_default) - return false; - } else { + case bpf_ctx_range(struct bpf_sock_addr, user_family): + case bpf_ctx_range(struct bpf_sock_addr, family): + case bpf_ctx_range(struct bpf_sock_addr, type): + case bpf_ctx_range(struct bpf_sock_addr, protocol): + if (type != BPF_READ) return false; - } + if (size != size_default) + return false; + break; + default: + return false; } return true; -- 2.43.0 Move the sizeof_field and offsetofend macros from individual test files to the common bpf_misc.h to avoid duplication. Acked-by: Eduard Zingerman Signed-off-by: Paul Chaignon --- tools/testing/selftests/bpf/progs/bpf_misc.h | 4 ++++ tools/testing/selftests/bpf/progs/test_cls_redirect.c | 4 +--- tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c | 5 +---- tools/testing/selftests/bpf/progs/verifier_ctx.c | 2 -- tools/testing/selftests/bpf/progs/verifier_sock.c | 4 ---- 5 files changed, 6 insertions(+), 13 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h index 7905396c9cc4..1004c4a64aaf 100644 --- a/tools/testing/selftests/bpf/progs/bpf_misc.h +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h @@ -167,6 +167,10 @@ #define __imm_ptr(name) [name]"r"(&name) #define __imm_insn(name, expr) [name]"i"(*(long *)&(expr)) +#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER)) +#define offsetofend(TYPE, MEMBER) \ + (offsetof(TYPE, MEMBER) + sizeof_field(TYPE, MEMBER)) + /* Magic constants used with __retval() */ #define POINTER_VALUE 0xbadcafe #define TEST_DATA_LEN 64 diff --git a/tools/testing/selftests/bpf/progs/test_cls_redirect.c b/tools/testing/selftests/bpf/progs/test_cls_redirect.c index 823169fb6e4c..26a53e54b8fa 100644 --- a/tools/testing/selftests/bpf/progs/test_cls_redirect.c +++ b/tools/testing/selftests/bpf/progs/test_cls_redirect.c @@ -22,6 +22,7 @@ #include "bpf_compiler.h" #include "test_cls_redirect.h" +#include "bpf_misc.h" #pragma GCC diagnostic ignored "-Waddress-of-packed-member" @@ -31,9 +32,6 @@ #define INLINING __always_inline #endif -#define offsetofend(TYPE, MEMBER) \ - (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER))) - #define IP_OFFSET_MASK (0x1FFF) #define IP_MF (0x2000) diff --git a/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c b/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c index 5f4e87ee949a..1ecdf4c54de4 100644 --- a/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c +++ b/tools/testing/selftests/bpf/progs/test_tcp_hdr_options.c @@ -14,10 +14,7 @@ #include #define BPF_PROG_TEST_TCP_HDR_OPTIONS #include "test_tcp_hdr_options.h" - -#ifndef sizeof_field -#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER)) -#endif +#include "bpf_misc.h" __u8 test_kind = TCPOPT_EXP; __u16 test_magic = 0xeB9F; diff --git a/tools/testing/selftests/bpf/progs/verifier_ctx.c b/tools/testing/selftests/bpf/progs/verifier_ctx.c index 424463094760..b927906aa305 100644 --- a/tools/testing/selftests/bpf/progs/verifier_ctx.c +++ b/tools/testing/selftests/bpf/progs/verifier_ctx.c @@ -5,8 +5,6 @@ #include #include "bpf_misc.h" -#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER)) - SEC("tc") __description("context stores via BPF_ATOMIC") __failure __msg("BPF_ATOMIC stores into R1 ctx is not allowed") diff --git a/tools/testing/selftests/bpf/progs/verifier_sock.c b/tools/testing/selftests/bpf/progs/verifier_sock.c index 0d5e56dffabb..bf88c644eb30 100644 --- a/tools/testing/selftests/bpf/progs/verifier_sock.c +++ b/tools/testing/selftests/bpf/progs/verifier_sock.c @@ -5,10 +5,6 @@ #include #include "bpf_misc.h" -#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER)) -#define offsetofend(TYPE, MEMBER) \ - (offsetof(TYPE, MEMBER) + sizeof_field(TYPE, MEMBER)) - struct { __uint(type, BPF_MAP_TYPE_REUSEPORT_SOCKARRAY); __uint(max_entries, 1); -- 2.43.0 This patch adds tests covering the various paddings in ctx structures. In case of sk_lookup BPF programs, the behavior is a bit different because accesses to the padding are explicitly allowed. Other cases result in a clear reject from the verifier. Acked-by: Eduard Zingerman Signed-off-by: Paul Chaignon --- .../selftests/bpf/progs/verifier_ctx.c | 30 +++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_ctx.c b/tools/testing/selftests/bpf/progs/verifier_ctx.c index b927906aa305..5ebf7d9bcc55 100644 --- a/tools/testing/selftests/bpf/progs/verifier_ctx.c +++ b/tools/testing/selftests/bpf/progs/verifier_ctx.c @@ -262,4 +262,34 @@ narrow_load("sockops", bpf_sock_ops, skb_hwtstamp); unaligned_access("flow_dissector", __sk_buff, data); unaligned_access("netfilter", bpf_nf_ctx, skb); +#define padding_access(type, ctx, prev_field, sz) \ + SEC(type) \ + __description("access on " #ctx " padding after " #prev_field) \ + __naked void padding_ctx_access_##ctx(void) \ + { \ + asm volatile (" \ + r1 = *(u%[size] *)(r1 + %[off]); \ + r0 = 0; \ + exit;" \ + : \ + : __imm_const(size, sz * 8), \ + __imm_const(off, offsetofend(struct ctx, prev_field)) \ + : __clobber_all); \ + } + +__failure __msg("invalid bpf_context access") +padding_access("cgroup/bind4", bpf_sock_addr, msg_src_ip6[3], 4); + +__success +padding_access("sk_lookup", bpf_sk_lookup, remote_port, 2); + +__failure __msg("invalid bpf_context access") +padding_access("tc", __sk_buff, tstamp_type, 2); + +__failure __msg("invalid bpf_context access") +padding_access("cgroup/post_bind4", bpf_sock, dst_port, 2); + +__failure __msg("invalid bpf_context access") +padding_access("sk_reuseport", sk_reuseport_md, hash, 4); + char _license[] SEC("license") = "GPL"; -- 2.43.0