The following BPF program, simplified from a syzkaller repro, causes a kernel warning: r0 = *(u8 *)(r1 + 169); exit; With pointer field sk being at offset 168 in __sk_buff. This access is detected as a narrower read in bpf_skb_is_valid_access because it doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed and later proceeds to bpf_convert_ctx_access. At that point, target_size is null and the verifier errors with a kernel warning and: verifier bug: error during ctx access conversion(1) This patch fixes that to return a proper "invalid bpf_context access off=X size=Y" error on the load instruction. The same issue affects multiple other fields in context structures that allow narrow access. Some other non-affected fields (for sk_msg, sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for consistency. Note this syzkaller crash was reported in [1], which used to be about a different bug, fixed in commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()"). Because syzbot somehow confused the two bugs, the new crash and repro didn't get reported to the mailing list. Link: https://syzkaller.appspot.com/bug?extid=0ef84a7bdf5301d4cbec [1] Fixes: f96da09473b52 ("bpf: simplify narrower ctx access") Fixes: 0df1a55afa832 ("bpf: Warn on internal verifier errors") Reported-by: syzbot+0ef84a7bdf5301d4cbec@syzkaller.appspotmail.com Signed-off-by: Paul Chaignon --- Changes in v2: - Use bpf_ctx_range{,_ptr} for a few other fields, for consistency, as suggested by Eduard and John. - Fix accesses to skb_hwtstamp, reported by Eduard. kernel/bpf/cgroup.c | 8 ++++---- net/core/filter.c | 20 ++++++++++---------- 2 files changed, 14 insertions(+), 14 deletions(-) diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 2e1c0eab20c0..180b630279b9 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -2577,22 +2577,22 @@ static bool cg_sockopt_is_valid_access(int off, int size, } switch (off) { - case offsetof(struct bpf_sockopt, sk): + case bpf_ctx_range_ptr(struct bpf_sockopt, sk): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_SOCKET; break; - case offsetof(struct bpf_sockopt, optval): + case bpf_ctx_range_ptr(struct bpf_sockopt, optval): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_PACKET; break; - case offsetof(struct bpf_sockopt, optval_end): + case bpf_ctx_range_ptr(struct bpf_sockopt, optval_end): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_PACKET_END; break; - case offsetof(struct bpf_sockopt, retval): + case bpf_ctx_range(struct bpf_sockopt, retval): if (size != size_default) return false; return prog->expected_attach_type == BPF_CGROUP_GETSOCKOPT; diff --git a/net/core/filter.c b/net/core/filter.c index 7a72f766aacf..47073a0180a4 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -8690,7 +8690,7 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type if (size != sizeof(__u64)) return false; break; - case offsetof(struct __sk_buff, sk): + case bpf_ctx_range_ptr(struct __sk_buff, sk): if (type == BPF_WRITE || size != sizeof(__u64)) return false; info->reg_type = PTR_TO_SOCK_COMMON_OR_NULL; @@ -9268,7 +9268,7 @@ static bool sock_addr_is_valid_access(int off, int size, return false; } break; - case offsetof(struct bpf_sock_addr, sk): + case bpf_ctx_range_ptr(struct bpf_sock_addr, sk): if (type != BPF_READ) return false; if (size != sizeof(__u64)) @@ -9318,17 +9318,17 @@ static bool sock_ops_is_valid_access(int off, int size, if (size != sizeof(__u64)) return false; break; - case offsetof(struct bpf_sock_ops, sk): + case bpf_ctx_range_ptr(struct bpf_sock_ops, sk): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_SOCKET_OR_NULL; break; - case offsetof(struct bpf_sock_ops, skb_data): + case bpf_ctx_range_ptr(struct bpf_sock_ops, skb_data): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_PACKET; break; - case offsetof(struct bpf_sock_ops, skb_data_end): + case bpf_ctx_range_ptr(struct bpf_sock_ops, skb_data_end): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_PACKET_END; @@ -9337,7 +9337,7 @@ static bool sock_ops_is_valid_access(int off, int size, bpf_ctx_record_field_size(info, size_default); return bpf_ctx_narrow_access_ok(off, size, size_default); - case offsetof(struct bpf_sock_ops, skb_hwtstamp): + case bpf_ctx_range(struct bpf_sock_ops, skb_hwtstamp): if (size != sizeof(__u64)) return false; break; @@ -9407,17 +9407,17 @@ static bool sk_msg_is_valid_access(int off, int size, return false; switch (off) { - case offsetof(struct sk_msg_md, data): + case bpf_ctx_range_ptr(struct sk_msg_md, data): info->reg_type = PTR_TO_PACKET; if (size != sizeof(__u64)) return false; break; - case offsetof(struct sk_msg_md, data_end): + case bpf_ctx_range_ptr(struct sk_msg_md, data_end): info->reg_type = PTR_TO_PACKET_END; if (size != sizeof(__u64)) return false; break; - case offsetof(struct sk_msg_md, sk): + case bpf_ctx_range_ptr(struct sk_msg_md, sk): if (size != sizeof(__u64)) return false; info->reg_type = PTR_TO_SOCKET; @@ -11623,7 +11623,7 @@ static bool sk_lookup_is_valid_access(int off, int size, return false; switch (off) { - case offsetof(struct bpf_sk_lookup, sk): + case bpf_ctx_range_ptr(struct bpf_sk_lookup, sk): info->reg_type = PTR_TO_SOCKET_OR_NULL; return size == sizeof(__u64); -- 2.43.0