* [PATCH net v2] net: skmsg: preserve sg.copy across SG transforms
@ 2026-06-10 6:21 Yiming Qian
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From: Yiming Qian @ 2026-06-10 6:21 UTC (permalink / raw)
To: security, John Fastabend, Jakub Sitnicki, Jakub Kicinski,
Sabrina Dubroca, David S . Miller, Eric Dumazet, Paolo Abeni,
Simon Horman
Cc: keenanat2000, yimingqian591, netdev, bpf, linux-kernel, stable
The sk_msg sg.copy bitmap is part of the scatterlist entry ownership
state. A set bit tells sk_msg_compute_data_pointers() not to expose the
entry through writable BPF ctx->data. This protects entries backed by
pages that are not private to the sk_msg, such as splice-backed file
page-cache pages.
Several sk_msg transform paths move, copy, split, or compact
msg->sg.data[] entries without moving the matching sg.copy bit. This can
make an externally backed entry arrive at a new slot with a clear copy
bit. A later SK_MSG verdict can then expose sg_virt(sge) as writable
ctx->data and BPF stores can modify the original page cache.
Keep sg.copy synchronized with sg.data[] whenever entries are
transferred, shifted, split, or copied into a new sk_msg. Clear the bit
when an entry is replaced by a newly allocated private page or freed.
This covers the BPF pull/push/pop helpers, sk_msg_shift_left/right(),
sk_msg_xfer(), and tls_split_open_record(), including the partial tail
entry created during TLS open-record splitting.
Fixes: d3b18ad31f93 ("tls: add bpf support to sk_msg handling")
Cc: stable@vger.kernel.org
Reported-by: Yiming Qian <yimingqian591@gmail.com>
Reported-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Yiming Qian <yimingqian591@gmail.com>
---
v2:
- Use __assign_bit() and the _assign helper suffix suggested in review.
- Broaden the fix beyond tls_split_open_record() to the sk_msg entry
transform paths in BPF pull/push/pop helpers, sk_msg shift helpers,
sk_msg_xfer(), and entry allocation/free cleanup.
- Expand the commit message to explain why sg.copy must move with the
scatterlist entry.
include/linux/skmsg.h | 15 +++++++++++----
net/core/filter.c | 27 +++++++++++++++++++++++++++
net/core/skmsg.c | 2 ++
net/tls/tls_sw.c | 4 ++++
4 files changed, 44 insertions(+), 4 deletions(-)
diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 19f4f253b4f90..937823856de59 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -4,6 +4,7 @@
#ifndef _LINUX_SKMSG_H
#define _LINUX_SKMSG_H
+#include <linux/bitops.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/scatterlist.h>
@@ -199,11 +200,14 @@ static inline void sk_msg_xfer(struct sk_msg *dst, struct sk_msg *src,
int which, u32 size)
{
dst->sg.data[which] = src->sg.data[which];
+ __assign_bit(which, dst->sg.copy, test_bit(which, src->sg.copy));
dst->sg.data[which].length = size;
dst->sg.size += size;
src->sg.size -= size;
src->sg.data[which].length -= size;
src->sg.data[which].offset += size;
+ if (!src->sg.data[which].length)
+ __clear_bit(which, src->sg.copy);
}
static inline void sk_msg_xfer_full(struct sk_msg *dst, struct sk_msg *src)
@@ -273,16 +277,19 @@ static inline void sk_msg_page_add(struct sk_msg *msg, struct page *page,
static inline void sk_msg_sg_copy(struct sk_msg *msg, u32 i, bool copy_state)
{
do {
- if (copy_state)
- __set_bit(i, msg->sg.copy);
- else
- __clear_bit(i, msg->sg.copy);
+ __assign_bit(i, msg->sg.copy, copy_state);
sk_msg_iter_var_next(i);
if (i == msg->sg.end)
break;
} while (1);
}
+static inline void sk_msg_sg_copy_assign(struct sk_msg *dst, u32 dst_i,
+ const struct sk_msg *src, u32 src_i)
+{
+ __assign_bit(dst_i, dst->sg.copy, test_bit(src_i, src->sg.copy));
+}
+
static inline void sk_msg_sg_copy_set(struct sk_msg *msg, u32 start)
{
sk_msg_sg_copy(msg, start, true);
diff --git a/net/core/filter.c b/net/core/filter.c
index 80439767e0eea..40037413dd4ec 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2733,11 +2733,13 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
poffset += len;
sge->length = 0;
put_page(sg_page(sge));
+ __clear_bit(i, msg->sg.copy);
sk_msg_iter_var_next(i);
} while (i != last_sge);
sg_set_page(&msg->sg.data[first_sge], page, copy, 0);
+ __clear_bit(first_sge, msg->sg.copy);
/* To repair sg ring we need to shift entries. If we only
* had a single entry though we can just replace it and
@@ -2763,9 +2765,11 @@ BPF_CALL_4(bpf_msg_pull_data, struct sk_msg *, msg, u32, start,
break;
msg->sg.data[i] = msg->sg.data[move_from];
+ sk_msg_sg_copy_assign(msg, i, msg, move_from);
msg->sg.data[move_from].length = 0;
msg->sg.data[move_from].page_link = 0;
msg->sg.data[move_from].offset = 0;
+ __clear_bit(move_from, msg->sg.copy);
sk_msg_iter_var_next(i);
} while (1);
@@ -2794,6 +2798,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
{
struct scatterlist sge, nsge, nnsge, rsge = {0}, *psge;
u32 new, i = 0, l = 0, space, copy = 0, offset = 0;
+ bool sge_copy, nsge_copy, nnsge_copy, rsge_copy = false;
u8 *raw, *to, *from;
struct page *page;
@@ -2866,6 +2871,7 @@ 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 = test_bit(i, msg->sg.copy);
psge->length = start - offset;
rsge.length -= psge->length;
@@ -2890,24 +2896,32 @@ 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);
+ sge_copy = test_bit(new, msg->sg.copy);
sg_unmark_end(&sge);
nsge = sk_msg_elem_cpy(msg, i);
+ nsge_copy = test_bit(i, msg->sg.copy);
if (rsge.length) {
sk_msg_iter_var_next(i);
nnsge = sk_msg_elem_cpy(msg, i);
+ nnsge_copy = test_bit(i, msg->sg.copy);
sk_msg_iter_next(msg, end);
}
while (i != msg->sg.end) {
msg->sg.data[i] = sge;
+ __assign_bit(i, msg->sg.copy, sge_copy);
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 = test_bit(i, msg->sg.copy);
} else {
nsge = sk_msg_elem_cpy(msg, i);
+ nsge_copy = test_bit(i, msg->sg.copy);
}
}
@@ -2921,6 +2935,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
get_page(sg_page(&rsge));
sk_msg_iter_var_next(new);
msg->sg.data[new] = rsge;
+ __assign_bit(new, msg->sg.copy, rsge_copy);
}
sk_msg_reset_curr(msg);
@@ -2948,25 +2963,33 @@ static void sk_msg_shift_left(struct sk_msg *msg, int i)
prev = i;
sk_msg_iter_var_next(i);
msg->sg.data[prev] = msg->sg.data[i];
+ sk_msg_sg_copy_assign(msg, prev, msg, i);
} while (i != msg->sg.end);
sk_msg_iter_prev(msg, end);
+ __clear_bit(msg->sg.end, msg->sg.copy);
}
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 = test_bit(i, msg->sg.copy);
sk_msg_iter_var_next(i);
tmp = sk_msg_elem_cpy(msg, i);
+ tmp_copy = test_bit(i, msg->sg.copy);
while (i != msg->sg.end) {
msg->sg.data[i] = sge;
+ __assign_bit(i, msg->sg.copy, sge_copy);
sk_msg_iter_var_next(i);
sge = tmp;
+ sge_copy = tmp_copy;
tmp = sk_msg_elem_cpy(msg, i);
+ tmp_copy = test_bit(i, msg->sg.copy);
}
}
@@ -3026,6 +3049,8 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
struct scatterlist *nsge, *sge = sk_msg_elem(msg, i);
int a = start - offset;
int b = sge->length - pop - a;
+ u32 sge_i = i;
+ bool sge_copy = test_bit(i, msg->sg.copy);
sk_msg_iter_var_next(i);
@@ -3038,6 +3063,7 @@ 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);
+ __assign_bit(i, msg->sg.copy, sge_copy);
} else {
struct page *page, *orig;
u8 *to, *from;
@@ -3054,6 +3080,7 @@ 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);
+ __clear_bit(sge_i, msg->sg.copy);
put_page(orig);
}
pop = 0;
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index e1850caf1a71a..30c3b9a2681c4 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -66,6 +66,7 @@ int sk_msg_alloc(struct sock *sk, struct sk_msg *msg, int len,
sge = &msg->sg.data[msg->sg.end];
sg_unmark_end(sge);
sg_set_page(sge, pfrag->page, use, orig_offset);
+ __clear_bit(msg->sg.end, msg->sg.copy);
get_page(pfrag->page);
sk_msg_iter_next(msg, end);
}
@@ -186,6 +187,7 @@ static int sk_msg_free_elem(struct sock *sk, struct sk_msg *msg, u32 i,
sk_mem_uncharge(sk, len);
put_page(sg_page(sge));
}
+ __clear_bit(i, msg->sg.copy);
memset(sge, 0, sizeof(*sge));
return len;
}
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 964ebc268ee46..a47f6a1e2c77d 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -623,6 +623,7 @@ static int tls_split_open_record(struct sock *sk, struct tls_rec *from,
struct scatterlist *sge, *osge, *nsge;
u32 orig_size = msg_opl->sg.size;
struct scatterlist tmp = { };
+ u32 tmp_i = 0;
struct sk_msg *msg_npl;
struct tls_rec *new;
int ret;
@@ -644,6 +645,7 @@ static int tls_split_open_record(struct sock *sk, struct tls_rec *from,
if (sge->length > apply) {
u32 len = sge->length - apply;
+ tmp_i = i;
get_page(sg_page(sge));
sg_set_page(&tmp, sg_page(sge), len,
sge->offset + apply);
@@ -675,6 +677,7 @@ static int tls_split_open_record(struct sock *sk, struct tls_rec *from,
nsge = sk_msg_elem(msg_npl, j);
if (tmp.length) {
memcpy(nsge, &tmp, sizeof(*nsge));
+ sk_msg_sg_copy_assign(msg_npl, j, msg_opl, tmp_i);
sk_msg_iter_var_next(j);
nsge = sk_msg_elem(msg_npl, j);
}
@@ -682,6 +685,7 @@ static int tls_split_open_record(struct sock *sk, struct tls_rec *from,
osge = sk_msg_elem(msg_opl, i);
while (osge->length) {
memcpy(nsge, osge, sizeof(*nsge));
+ sk_msg_sg_copy_assign(msg_npl, j, msg_opl, i);
sg_unmark_end(nsge);
sk_msg_iter_var_next(i);
sk_msg_iter_var_next(j);
--
2.34.1
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