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bpf, sockmap: keep sk_msg copy state in sync

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SK_MSG uses msg->sg.copy as per-scatterlist-entry provenance. Entries
with this bit set are copied before data/data_end are exposed to SK_MSG
BPF programs for direct packet access.

bpf_msg_pull_data(), bpf_msg_push_data(), and bpf_msg_pop_data()
rewrite the sk_msg scatterlist ring by collapsing, splitting, and
shifting entries. These operations move msg->sg.data[] entries, but the
parallel copy bitmap can be left behind on the old slot. A copied entry
can then return to msg->sg.start with its copy bit clear and be exposed
as directly writable packet data.

This corruption path requires an attached SK_MSG BPF program that calls
the mutating helpers; ordinary sockmap/TLS traffic that never runs
push/pop/pull helper sequences is not affected.

Keep msg->sg.copy synchronized with scatterlist entry moves, preserve
the copy bit when an entry is split, clear it when a helper replaces an
entry with a private page, and clear slots vacated by pull-data
compaction.

Fixes: 015632bb30 ("bpf: sk_msg program helper bpf_sk_msg_pull_data")
Fixes: 6fff607e2f ("bpf: sk_msg program helper bpf_msg_push_data")
Fixes: 7246d8ed4d ("bpf: helper to pop data from messages")
Cc: stable@vger.kernel.org
Co-developed-by: Han Guidong <2045gemini@gmail.com>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Han Guidong <2045gemini@gmail.com>
Signed-off-by: Zhang Cen <rollkingzzc@gmail.com>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/r/20260615021959.140010-4-jiayuan.chen@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Zhang Cen 2026-06-15 10:19:56 +08:00 committed by Alexei Starovoitov
parent f3f34ca45b
commit 2ccbc9a387
1 changed files with 83 additions and 5 deletions
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88
net/core/filter.c
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@ -2654,6 +2654,38 @@ static void sk_msg_reset_curr(struct sk_msg *msg)
}
}
static bool sk_msg_elem_is_copy(const struct sk_msg *msg, u32 i)
{
return test_bit(i, msg->sg.copy);
}
static void sk_msg_clear_elem_copy(struct sk_msg *msg, u32 i)
{
__clear_bit(i, msg->sg.copy);
}
static void sk_msg_set_elem_copy(struct sk_msg *msg, u32 i)
{
__set_bit(i, msg->sg.copy);
}
static void sk_msg_clear_copy_range(struct sk_msg *msg, u32 start, u32 end)
{
while (start != end) {
sk_msg_clear_elem_copy(msg, start);
sk_msg_iter_var_next(start);
}
}
static void sk_msg_sg_move(struct sk_msg *msg, u32 dst, u32 src)
{
msg->sg.data[dst] = msg->sg.data[src];
if (sk_msg_elem_is_copy(msg, src))
sk_msg_set_elem_copy(msg, dst);
else
sk_msg_clear_elem_copy(msg, dst);
}
static const struct bpf_func_proto bpf_msg_cork_bytes_proto = {
.func = bpf_msg_cork_bytes,
.gpl_only = false,
@ -2692,7 +2724,7 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
* account for the headroom.
*/
bytes_sg_total = start - offset + bytes;
if (!test_bit(i, msg->sg.copy) && bytes_sg_total <= len)
if (!sk_msg_elem_is_copy(msg, i) && bytes_sg_total <= len)
goto out;
/* At this point we need to linearize multiple scatterlist
@ -2738,6 +2770,7 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
} while (i != last_sge);
sg_set_page(&msg->sg.data[first_sge], page, copy, 0);
sk_msg_clear_elem_copy(msg, first_sge);
/* To repair sg ring we need to shift entries. If we only
* had a single entry though we can just replace it and
@ -2747,8 +2780,14 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
shift = last_sge > first_sge ?
last_sge - first_sge - 1 :
NR_MSG_FRAG_IDS - first_sge + last_sge - 1;
if (!shift)
if (!shift) {
sk_msg_clear_elem_copy(msg, msg->sg.end);
goto out;
}
i = first_sge;
sk_msg_iter_var_next(i);
sk_msg_clear_copy_range(msg, i, last_sge);
i = first_sge;
sk_msg_iter_var_next(i);
@ -2762,16 +2801,18 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
if (move_from == msg->sg.end)
break;
msg->sg.data[i] = msg->sg.data[move_from];
sk_msg_sg_move(msg, i, move_from);
msg->sg.data[move_from].length = 0;
msg->sg.data[move_from].page_link = 0;
msg->sg.data[move_from].offset = 0;
sk_msg_clear_elem_copy(msg, move_from);
sk_msg_iter_var_next(i);
} while (1);
msg->sg.end = msg->sg.end - shift > msg->sg.end ?
msg->sg.end - shift + NR_MSG_FRAG_IDS :
msg->sg.end - shift;
sk_msg_clear_elem_copy(msg, msg->sg.end);
out:
sk_msg_reset_curr(msg);
msg->data = sg_virt(&msg->sg.data[first_sge]) + start - offset;
@ -2792,8 +2833,10 @@ static const struct bpf_func_proto bpf_msg_pull_data_proto = {
BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
u32, len, u64, flags)
{
bool sge_copy = false, nsge_copy = false, nnsge_copy = false;
struct scatterlist sge, nsge, nnsge, rsge = {0}, *psge;
u32 new, i = 0, l = 0, space, copy = 0, offset = 0;
bool rsge_copy = false;
u8 *raw, *to, *from;
struct page *page;
@ -2869,6 +2912,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
sk_msg_iter_var_prev(i);
psge = sk_msg_elem(msg, i);
rsge = sk_msg_elem_cpy(msg, i);
rsge_copy = sk_msg_elem_is_copy(msg, i);
psge->length = start - offset;
rsge.length -= psge->length;
@ -2894,23 +2938,34 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
/* Shift one or two slots as needed */
sge = sk_msg_elem_cpy(msg, new);
sg_unmark_end(&sge);
sge_copy = sk_msg_elem_is_copy(msg, new);
nsge = sk_msg_elem_cpy(msg, i);
nsge_copy = sk_msg_elem_is_copy(msg, i);
if (rsge.length) {
sk_msg_iter_var_next(i);
nnsge = sk_msg_elem_cpy(msg, i);
nnsge_copy = sk_msg_elem_is_copy(msg, i);
sk_msg_iter_next(msg, end);
}
while (i != msg->sg.end) {
msg->sg.data[i] = sge;
if (sge_copy)
sk_msg_set_elem_copy(msg, i);
else
sk_msg_clear_elem_copy(msg, i);
sge = nsge;
sge_copy = nsge_copy;
sk_msg_iter_var_next(i);
if (rsge.length) {
nsge = nnsge;
nsge_copy = nnsge_copy;
nnsge = sk_msg_elem_cpy(msg, i);
nnsge_copy = sk_msg_elem_is_copy(msg, i);
} else {
nsge = sk_msg_elem_cpy(msg, i);
nsge_copy = sk_msg_elem_is_copy(msg, i);
}
}
@ -2918,13 +2973,18 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
/* Place newly allocated data buffer */
sk_mem_charge(msg->sk, len);
msg->sg.size += len;
__clear_bit(new, msg->sg.copy);
sk_msg_clear_elem_copy(msg, new);
sg_set_page(&msg->sg.data[new], page, len + copy, 0);
if (rsge.length) {
get_page(sg_page(&rsge));
sk_msg_iter_var_next(new);
msg->sg.data[new] = rsge;
if (rsge_copy)
sk_msg_set_elem_copy(msg, new);
else
sk_msg_clear_elem_copy(msg, new);
}
sk_msg_clear_elem_copy(msg, msg->sg.end);
sk_msg_reset_curr(msg);
sk_msg_compute_data_pointers(msg);
@ -2950,27 +3010,38 @@ static void sk_msg_shift_left(struct sk_msg *msg, int i)
do {
prev = i;
sk_msg_iter_var_next(i);
msg->sg.data[prev] = msg->sg.data[i];
sk_msg_sg_move(msg, prev, i);
} while (i != msg->sg.end);
sk_msg_iter_prev(msg, end);
sk_msg_clear_elem_copy(msg, msg->sg.end);
}
static void sk_msg_shift_right(struct sk_msg *msg, int i)
{
struct scatterlist tmp, sge;
bool tmp_copy, sge_copy;
sk_msg_iter_next(msg, end);
sge = sk_msg_elem_cpy(msg, i);
sge_copy = sk_msg_elem_is_copy(msg, i);
sk_msg_iter_var_next(i);
tmp = sk_msg_elem_cpy(msg, i);
tmp_copy = sk_msg_elem_is_copy(msg, i);
while (i != msg->sg.end) {
msg->sg.data[i] = sge;
if (sge_copy)
sk_msg_set_elem_copy(msg, i);
else
sk_msg_clear_elem_copy(msg, i);
sk_msg_iter_var_next(i);
sge = tmp;
sge_copy = tmp_copy;
tmp = sk_msg_elem_cpy(msg, i);
tmp_copy = sk_msg_elem_is_copy(msg, i);
}
sk_msg_clear_elem_copy(msg, msg->sg.end);
}
BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
@ -3027,8 +3098,10 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
*/
if (start != offset) {
struct scatterlist *nsge, *sge = sk_msg_elem(msg, i);
bool sge_copy = sk_msg_elem_is_copy(msg, i);
int a = start - offset;
int b = sge->length - pop - a;
u32 sge_idx = i;
sk_msg_iter_var_next(i);
@ -3041,6 +3114,10 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
sg_set_page(nsge,
sg_page(sge),
b, sge->offset + pop + a);
if (sge_copy)
sk_msg_set_elem_copy(msg, i);
else
sk_msg_clear_elem_copy(msg, i);
} else {
struct page *page, *orig;
u8 *to, *from;
@ -3057,6 +3134,7 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
memcpy(to, from, a);
memcpy(to + a, from + a + pop, b);
sg_set_page(sge, page, a + b, 0);
sk_msg_clear_elem_copy(msg, sge_idx);
put_page(orig);
}
pop = 0;