[PATCH 5.10 114/161] bpf: Reject narrower access to pointer ctx fields

Greg Kroah-Hartman
2026-02-04T14:48:44Z

From: Paul Chaignon <paul.chaignon@gmail.com>

commit e09299225d5ba3916c91ef70565f7d2187e4cca0 upstream.

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. Note that for the
"is_narrower_load" case in the convert_ctx_accesses(), the insn->off
is aligned, so the cnt may not be 0 because it matches the
offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However,
the target_size stays 0 and the verifier errors with a kernel warning:

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 the "Closes" link below, 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.

Fixes: f96da09473b52 ("bpf: simplify narrower ctx access")
Fixes: 0df1a55afa832 ("bpf: Warn on internal verifier errors")
Reported-by: syzbot+0ef84a7bdf5301d4cbec@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0ef84a7bdf5301d4cbec
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://patch.msgid.link/3b8dcee67ff4296903351a974ddd9c4dca768b64.1753194596.git.paul.chaignon@gmail.com
[shung-hsi.yu: offset(struct bpf_sock_ops, skb_hwtstamp) case was
dropped becasuse it was only added in v6.2 with commit 9bb053490f1a
("bpf: Add hwtstamp field for the sockops prog")]
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/bpf/cgroup.c | 8 ++++----
net/core/filter.c | 18 +++++++++---------
2 files changed, 13 insertions(+), 13 deletions(-)

--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1915,22 +1915,22 @@ static bool cg_sockopt_is_valid_access(i
}

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;
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7634,7 +7634,7 @@ static bool bpf_skb_is_valid_access(int
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;
@@ -8151,7 +8151,7 @@ static bool sock_addr_is_valid_access(in
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))
@@ -8205,17 +8205,17 @@ static bool sock_ops_is_valid_access(int
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;
@@ -8289,17 +8289,17 @@ static bool sk_msg_is_valid_access(int o
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;
@@ -10324,7 +10324,7 @@ static bool sk_lookup_is_valid_access(in
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);