diff options
| author | Jiayuan Chen <jiayuan.chen@linux.dev> | 2026-09-03 18:09:20 +0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-09-12 11:11:10 -0700 |
| commit | 75f8cf22463d82bb1fb0239a3d485fc8f4c8ef03 (patch) | |
| tree | eb5e15b62c267bcd7cca8e238109e107a9a92187 /net | |
| parent | 85136bf22404474a815fc0ed26ec0d1cbc1bc3f9 (diff) | |
bpf: Fix out-of-bounds read of rtt_min in sock_ops
A sockops prog reading skops->rtt_min never checks the sk type: on the
tcp_conn_request() path sock_ops->sk is a request_sock (non-full), and the
ctx rewrite casts it to a tcp_sock (full) and reads rtt_min past the end of
the request_sock, returning dirty adjacent memory.
SEC("sockops")
int prog(struct bpf_sock_ops *skops)
{
switch (skops->op) {
case BPF_SOCK_OPS_RWND_INIT:
leak = skops->rtt_min; /* reads the request_sock OOB */
...
}
}
For instance one such read returned rtt_min=0xffff8881, the high half of a
leaked kernel pointer.
Guarding that cast is exactly what SOCK_OPS_GET_FIELD() does -- it checks
is_locked_tcp_sock and returns 0 when sock_ops->sk is not a locked full
socket. Every other tcp_sock field in sock_ops goes through it; rtt_min is
the only one open-coded, so it skips the check.
Read rtt_min through SOCK_OPS_GET_FIELD() too. rtt_min is a bit special:
it is a struct minmax and we only want the current min, so pass
rtt_min.s[0].v. That is equivalent to the old hand-computed offset
offsetof(struct tcp_sock, rtt_min) + sizeof_field(struct minmax_sample, t)
(s[0] sits at rtt_min + 0 and .v at + sizeof(.t), i.e. what minmax_get()
returns), so the loaded field is unchanged and only the full-sock guard is
added. The two BUILD_BUG_ON()s that protected the hand-computed offset
are no longer needed.
Before patch:
0: r1 = *(u64 *)(r1 +0) ; r1 = skops->sk
1: r1 = *(u32 *)(r1 +2324) ; ((tcp_sock *)sk)->rtt_min.s[0].v
After patch:
0: *(u64 *)(r1 +56) = r9
1: r9 = *(u8 *)(r1 +50) ; is_locked_tcp_sock
2: if r9 == 0 goto pc+4 ; not a locked full sock -> 0
3: r9 = *(u64 *)(r1 +56)
4: r1 = *(u64 *)(r1 +0) ; r1 = skops->sk
5: r1 = *(u32 *)(r1 +2324) ; rtt_min.s[0].v
6: goto pc+2
7: r9 = *(u64 *)(r1 +56)
8: r1 = 0
Fixes: 44f0e43037d3 ("bpf: Add support for reading sk_state and more")
Reported-by: VEGA <vega@nebusec.ai>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260903100921.113374-1-jiayuan.chen@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/core/filter.c | 13 |
1 files changed, 1 insertions, 12 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index cae43b999162..532405988fd9 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -11106,18 +11106,7 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type, break; case offsetof(struct bpf_sock_ops, rtt_min): - BUILD_BUG_ON(sizeof_field(struct tcp_sock, rtt_min) != - sizeof(struct minmax)); - BUILD_BUG_ON(sizeof(struct minmax) < - sizeof(struct minmax_sample)); - - *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( - struct bpf_sock_ops_kern, sk), - si->dst_reg, si->src_reg, - offsetof(struct bpf_sock_ops_kern, sk)); - *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg, - offsetof(struct tcp_sock, rtt_min) + - sizeof_field(struct minmax_sample, t)); + SOCK_OPS_GET_FIELD(rtt_min, rtt_min.s[0].v, struct tcp_sock); break; case offsetof(struct bpf_sock_ops, bpf_sock_ops_cb_flags): |