* [PATCH v2] net: bonding: fix use-after-free in bond_xmit_broadcast()
[not found] <20260428104138.reply-bonding-6.12@kernel.org>
@ 2026-04-28 16:32 ` Kevin Berry
2026-04-28 22:41 ` Xiang Mei
0 siblings, 1 reply; 4+ messages in thread
From: Kevin Berry @ 2026-04-28 16:32 UTC (permalink / raw)
To: xmei5; +Cc: bestswngs, chenglongtang, joneslee, kpberry, pabeni, rnj, stable
From: Xiang Mei <xmei5@asu.edu>
bond_xmit_broadcast() reuses the original skb for the last slave
(determined by bond_is_last_slave()) and clones it for others.
Concurrent slave enslave/release can mutate the slave list during
RCU-protected iteration, changing which slave is "last" mid-loop.
This causes the original skb to be double-consumed (double-freed).
Replace the racy bond_is_last_slave() check with a simple index
comparison (i + 1 == slaves_count) against the pre-snapshot slave
count taken via READ_ONCE() before the loop. This preserves the
zero-copy optimization for the last slave while making the "last"
determination stable against concurrent list mutations.
The UAF can trigger the following crash:
==================================================================
BUG: KASAN: slab-use-after-free in skb_clone
Read of size 8 at addr ffff888100ef8d40 by task exploit/147
CPU: 1 UID: 0 PID: 147 Comm: exploit Not tainted 7.0.0-rc3+ #4 PREEMPTLAZY
Call Trace:
<TASK>
dump_stack_lvl (lib/dump_stack.c:123)
print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
kasan_report (mm/kasan/report.c:597)
skb_clone (include/linux/skbuff.h:1724 include/linux/skbuff.h:1792 include/linux/skbuff.h:3396 net/core/skbuff.c:2108)
bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5334)
bond_start_xmit (drivers/net/bonding/bond_main.c:5567 drivers/net/bonding/bond_main.c:5593)
dev_hard_start_xmit (include/linux/netdevice.h:5325 include/linux/netdevice.h:5334 net/core/dev.c:3871 net/core/dev.c:3887)
__dev_queue_xmit (include/linux/netdevice.h:3601 net/core/dev.c:4838)
ip6_finish_output2 (include/net/neighbour.h:540 include/net/neighbour.h:554 net/ipv6/ip6_output.c:136)
ip6_finish_output (net/ipv6/ip6_output.c:208 net/ipv6/ip6_output.c:219)
ip6_output (net/ipv6/ip6_output.c:250)
ip6_send_skb (net/ipv6/ip6_output.c:1985)
udp_v6_send_skb (net/ipv6/udp.c:1442)
udpv6_sendmsg (net/ipv6/udp.c:1733)
__sys_sendto (net/socket.c:730 net/socket.c:742 net/socket.c:2206)
__x64_sys_sendto (net/socket.c:2209)
do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
</TASK>
Allocated by task 147:
Freed by task 147:
The buggy address belongs to the object at ffff888100ef8c80
which belongs to the cache skbuff_head_cache of size 224
The buggy address is located 192 bytes inside of
freed 224-byte region [ffff888100ef8c80, ffff888100ef8d60)
Memory state around the buggy address:
ffff888100ef8c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
ffff888100ef8c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888100ef8d00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
^
ffff888100ef8d80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
ffff888100ef8e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Fixes: 4e5bd03ae346 ("net: bonding: fix bond_xmit_broadcast return value error bug")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Link: https://patch.msgid.link/20260326075553.3960562-1-xmei5@asu.edu
Signed-off-by: Kevin Berry <kpberry@google.com>
---
drivers/net/bonding/bond_main.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 5035cfa74f1a..9f1a189d46f1 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -5326,14 +5326,21 @@ static netdev_tx_t bond_xmit_broadcast(struct sk_buff *skb,
struct list_head *iter;
bool xmit_suc = false;
bool skb_used = false;
+ int slaves_count, i = 0;
+ slaves_count = READ_ONCE(bond->slave_cnt);
bond_for_each_slave_rcu(bond, slave, iter) {
struct sk_buff *skb2;
+ bool is_last;
+
+ if (++i > slaves_count)
+ break;
+ is_last = (i == slaves_count);
if (!(bond_slave_is_up(slave) && slave->link == BOND_LINK_UP))
continue;
- if (bond_is_last_slave(bond, slave)) {
+ if (is_last) {
skb2 = skb;
skb_used = true;
} else {
base-commit: c286ea5e62389897291fa742d2bb909ecc9ef2d0
--
2.54.0.545.g6539524ca2-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] net: bonding: fix use-after-free in bond_xmit_broadcast()
2026-04-28 16:32 ` [PATCH v2] net: bonding: fix use-after-free in bond_xmit_broadcast() Kevin Berry
@ 2026-04-28 22:41 ` Xiang Mei
2026-05-06 20:28 ` Kevin Berry
0 siblings, 1 reply; 4+ messages in thread
From: Xiang Mei @ 2026-04-28 22:41 UTC (permalink / raw)
To: Kevin Berry; +Cc: bestswngs, chenglongtang, joneslee, pabeni, rnj, stable
Thanks Kevin for picking this up for 6.12.y.
We can't backport the upstream patch since the upstream rewrite that
introduced the bond_up_slave snapshot array isn't in this tree.
Confirmed it fixes the double-free without introducing concerning side effects.
Acked-by: Xiang Mei <xmei5@asu.edu>
On Tue, Apr 28, 2026 at 9:32 AM Kevin Berry <kpberry@google.com> wrote:
>
> From: Xiang Mei <xmei5@asu.edu>
>
> bond_xmit_broadcast() reuses the original skb for the last slave
> (determined by bond_is_last_slave()) and clones it for others.
> Concurrent slave enslave/release can mutate the slave list during
> RCU-protected iteration, changing which slave is "last" mid-loop.
> This causes the original skb to be double-consumed (double-freed).
>
> Replace the racy bond_is_last_slave() check with a simple index
> comparison (i + 1 == slaves_count) against the pre-snapshot slave
> count taken via READ_ONCE() before the loop. This preserves the
> zero-copy optimization for the last slave while making the "last"
> determination stable against concurrent list mutations.
>
> The UAF can trigger the following crash:
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in skb_clone
> Read of size 8 at addr ffff888100ef8d40 by task exploit/147
>
> CPU: 1 UID: 0 PID: 147 Comm: exploit Not tainted 7.0.0-rc3+ #4 PREEMPTLAZY
> Call Trace:
> <TASK>
> dump_stack_lvl (lib/dump_stack.c:123)
> print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
> kasan_report (mm/kasan/report.c:597)
> skb_clone (include/linux/skbuff.h:1724 include/linux/skbuff.h:1792 include/linux/skbuff.h:3396 net/core/skbuff.c:2108)
> bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5334)
> bond_start_xmit (drivers/net/bonding/bond_main.c:5567 drivers/net/bonding/bond_main.c:5593)
> dev_hard_start_xmit (include/linux/netdevice.h:5325 include/linux/netdevice.h:5334 net/core/dev.c:3871 net/core/dev.c:3887)
> __dev_queue_xmit (include/linux/netdevice.h:3601 net/core/dev.c:4838)
> ip6_finish_output2 (include/net/neighbour.h:540 include/net/neighbour.h:554 net/ipv6/ip6_output.c:136)
> ip6_finish_output (net/ipv6/ip6_output.c:208 net/ipv6/ip6_output.c:219)
> ip6_output (net/ipv6/ip6_output.c:250)
> ip6_send_skb (net/ipv6/ip6_output.c:1985)
> udp_v6_send_skb (net/ipv6/udp.c:1442)
> udpv6_sendmsg (net/ipv6/udp.c:1733)
> __sys_sendto (net/socket.c:730 net/socket.c:742 net/socket.c:2206)
> __x64_sys_sendto (net/socket.c:2209)
> do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
> entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> </TASK>
>
> Allocated by task 147:
>
> Freed by task 147:
>
> The buggy address belongs to the object at ffff888100ef8c80
> which belongs to the cache skbuff_head_cache of size 224
> The buggy address is located 192 bytes inside of
> freed 224-byte region [ffff888100ef8c80, ffff888100ef8d60)
>
> Memory state around the buggy address:
> ffff888100ef8c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
> ffff888100ef8c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff888100ef8d00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ^
> ffff888100ef8d80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
> ffff888100ef8e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> Fixes: 4e5bd03ae346 ("net: bonding: fix bond_xmit_broadcast return value error bug")
> Reported-by: Weiming Shi <bestswngs@gmail.com>
> Signed-off-by: Xiang Mei <xmei5@asu.edu>
> Link: https://patch.msgid.link/20260326075553.3960562-1-xmei5@asu.edu
> Signed-off-by: Kevin Berry <kpberry@google.com>
> ---
> drivers/net/bonding/bond_main.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 5035cfa74f1a..9f1a189d46f1 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -5326,14 +5326,21 @@ static netdev_tx_t bond_xmit_broadcast(struct sk_buff *skb,
> struct list_head *iter;
> bool xmit_suc = false;
> bool skb_used = false;
> + int slaves_count, i = 0;
>
> + slaves_count = READ_ONCE(bond->slave_cnt);
> bond_for_each_slave_rcu(bond, slave, iter) {
> struct sk_buff *skb2;
> + bool is_last;
> +
> + if (++i > slaves_count)
> + break;
> + is_last = (i == slaves_count);
>
> if (!(bond_slave_is_up(slave) && slave->link == BOND_LINK_UP))
> continue;
>
> - if (bond_is_last_slave(bond, slave)) {
> + if (is_last) {
> skb2 = skb;
> skb_used = true;
> } else {
>
> base-commit: c286ea5e62389897291fa742d2bb909ecc9ef2d0
> --
> 2.54.0.545.g6539524ca2-goog
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] net: bonding: fix use-after-free in bond_xmit_broadcast()
2026-04-28 22:41 ` Xiang Mei
@ 2026-05-06 20:28 ` Kevin Berry
2026-05-06 20:28 ` [PATCH] " Kevin Berry
0 siblings, 1 reply; 4+ messages in thread
From: Kevin Berry @ 2026-05-06 20:28 UTC (permalink / raw)
To: xmei5; +Cc: bestswngs, chenglongtang, joneslee, kpberry, pabeni, rnj, stable
Hi all,
Sending the patch for 6.6 as well since it should be the same as
the 6.12 patch. Tested by compiling.
Thanks,
Kevin
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] net: bonding: fix use-after-free in bond_xmit_broadcast()
2026-05-06 20:28 ` Kevin Berry
@ 2026-05-06 20:28 ` Kevin Berry
0 siblings, 0 replies; 4+ messages in thread
From: Kevin Berry @ 2026-05-06 20:28 UTC (permalink / raw)
To: xmei5
Cc: bestswngs, chenglongtang, joneslee, kpberry, pabeni, rnj, stable,
Sasha Levin, Greg Kroah-Hartman
From: Xiang Mei <xmei5@asu.edu>
commit 2884bf72fb8f03409e423397319205de48adca16 upstream.
bond_xmit_broadcast() reuses the original skb for the last slave
(determined by bond_is_last_slave()) and clones it for others.
Concurrent slave enslave/release can mutate the slave list during
RCU-protected iteration, changing which slave is "last" mid-loop.
This causes the original skb to be double-consumed (double-freed).
Replace the racy bond_is_last_slave() check with a simple index
comparison (i + 1 == slaves_count) against the pre-snapshot slave
count taken via READ_ONCE() before the loop. This preserves the
zero-copy optimization for the last slave while making the "last"
determination stable against concurrent list mutations.
The UAF can trigger the following crash:
==================================================================
BUG: KASAN: slab-use-after-free in skb_clone
Read of size 8 at addr ffff888100ef8d40 by task exploit/147
CPU: 1 UID: 0 PID: 147 Comm: exploit Not tainted 7.0.0-rc3+ #4 PREEMPTLAZY
Call Trace:
<TASK>
dump_stack_lvl (lib/dump_stack.c:123)
print_report (mm/kasan/report.c:379 mm/kasan/report.c:482)
kasan_report (mm/kasan/report.c:597)
skb_clone (include/linux/skbuff.h:1724 include/linux/skbuff.h:1792 include/linux/skbuff.h:3396 net/core/skbuff.c:2108)
bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5334)
bond_start_xmit (drivers/net/bonding/bond_main.c:5567 drivers/net/bonding/bond_main.c:5593)
dev_hard_start_xmit (include/linux/netdevice.h:5325 include/linux/netdevice.h:5334 net/core/dev.c:3871 net/core/dev.c:3887)
__dev_queue_xmit (include/linux/netdevice.h:3601 net/core/dev.c:4838)
ip6_finish_output2 (include/net/neighbour.h:540 include/net/neighbour.h:554 net/ipv6/ip6_output.c:136)
ip6_finish_output (net/ipv6/ip6_output.c:208 net/ipv6/ip6_output.c:219)
ip6_output (net/ipv6/ip6_output.c:250)
ip6_send_skb (net/ipv6/ip6_output.c:1985)
udp_v6_send_skb (net/ipv6/udp.c:1442)
udpv6_sendmsg (net/ipv6/udp.c:1733)
__sys_sendto (net/socket.c:730 net/socket.c:742 net/socket.c:2206)
__x64_sys_sendto (net/socket.c:2209)
do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
</TASK>
Allocated by task 147:
Freed by task 147:
The buggy address belongs to the object at ffff888100ef8c80
which belongs to the cache skbuff_head_cache of size 224
The buggy address is located 192 bytes inside of
freed 224-byte region [ffff888100ef8c80, ffff888100ef8d60)
Memory state around the buggy address:
ffff888100ef8c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
ffff888100ef8c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888100ef8d00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
^
ffff888100ef8d80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
ffff888100ef8e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Fixes: 4e5bd03ae346 ("net: bonding: fix bond_xmit_broadcast return value error bug")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Link: https://patch.msgid.link/20260326075553.3960562-1-xmei5@asu.edu
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kevin Berry <kpberry@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/bonding/bond_main.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 114ebaa284da..6484ba1ab14c 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -5280,18 +5280,22 @@ static netdev_tx_t bond_xmit_broadcast(struct sk_buff *skb,
struct net_device *bond_dev)
{
struct bonding *bond = netdev_priv(bond_dev);
- struct slave *slave = NULL;
- struct list_head *iter;
+ struct bond_up_slave *slaves;
bool xmit_suc = false;
bool skb_used = false;
+ int slaves_count, i;
- bond_for_each_slave_rcu(bond, slave, iter) {
+ slaves = rcu_dereference(bond->all_slaves);
+
+ slaves_count = slaves ? READ_ONCE(slaves->count) : 0;
+ for (i = 0; i < slaves_count; i++) {
+ struct slave *slave = slaves->arr[i];
struct sk_buff *skb2;
if (!(bond_slave_is_up(slave) && slave->link == BOND_LINK_UP))
continue;
- if (bond_is_last_slave(bond, slave)) {
+ if (i + 1 == slaves_count) {
skb2 = skb;
skb_used = true;
} else {
base-commit: 258cf62a6dfde3c6a39d120a56a298f2ed6a8901
--
2.54.0.563.g4f69b47b94-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-05-06 20:28 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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[not found] <20260428104138.reply-bonding-6.12@kernel.org>
2026-04-28 16:32 ` [PATCH v2] net: bonding: fix use-after-free in bond_xmit_broadcast() Kevin Berry
2026-04-28 22:41 ` Xiang Mei
2026-05-06 20:28 ` Kevin Berry
2026-05-06 20:28 ` [PATCH] " Kevin Berry
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