* [PATCH net] ipv6: mcast: Fix use-after-free when processing MLD queries
@ 2026-06-03 10:18 Ido Schimmel
2026-06-03 10:54 ` Eric Dumazet
2026-06-03 11:45 ` Jiayuan Chen
0 siblings, 2 replies; 3+ messages in thread
From: Ido Schimmel @ 2026-06-03 10:18 UTC (permalink / raw)
To: netdev; +Cc: davem, kuba, pabeni, edumazet, horms, dsahern, leo, Ido Schimmel
When processing an MLD query, a pointer to the multicast group address
is retrieved when initially parsing the packet. This pointer is later
dereferenced without being reloaded despite the fact that the skb header
might have been reallocated following the pskb_may_pull() calls, leading
to a use-after-free [1].
Fix by copying the multicast group address when the packet is initially
parsed.
[1]
BUG: KASAN: slab-use-after-free in __mld_query_work (net/ipv6/mcast.c:1512)
Read of size 8 at addr ffff8881154b8e90 by task kworker/4:1/118
Workqueue: mld mld_query_work
Call Trace:
<TASK>
dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
print_address_description.constprop.0 (mm/kasan/report.c:378)
print_report (mm/kasan/report.c:482)
kasan_report (mm/kasan/report.c:595)
__mld_query_work (net/ipv6/mcast.c:1512)
mld_query_work (net/ipv6/mcast.c:1563)
process_one_work (kernel/workqueue.c:3314)
worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
kthread (kernel/kthread.c:436)
ret_from_fork (arch/x86/kernel/process.c:158)
ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
</TASK>
[...]
Freed by task 118:
kasan_save_stack (mm/kasan/common.c:57)
kasan_save_track (mm/kasan/common.c:78)
kasan_save_free_info (mm/kasan/generic.c:584)
__kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566)
pskb_expand_head (net/core/skbuff.c:2335)
__pskb_pull_tail (net/core/skbuff.c:2878 (discriminator 4))
__mld_query_work (net/ipv6/mcast.c:1495 (discriminator 1))
mld_query_work (net/ipv6/mcast.c:1563)
process_one_work (kernel/workqueue.c:3314)
worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
kthread (kernel/kthread.c:436)
ret_from_fork (arch/x86/kernel/process.c:158)
ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
Fixes: 97300b5fdfe2 ("[MCAST] IPv6: Check packet size when process Multicast")
Reported-by: Leo Lin <leo@depthfirst.com>
Reviewed-by: David Ahern <dahern@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---
net/ipv6/mcast.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 3330adcf26db..d9b855d5191b 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1424,9 +1424,9 @@ void igmp6_event_query(struct sk_buff *skb)
static void __mld_query_work(struct sk_buff *skb)
{
struct mld2_query *mlh2 = NULL;
- const struct in6_addr *group;
unsigned long max_delay;
struct inet6_dev *idev;
+ struct in6_addr group;
struct ifmcaddr6 *ma;
struct mld_msg *mld;
int group_type;
@@ -1458,8 +1458,8 @@ static void __mld_query_work(struct sk_buff *skb)
goto kfree_skb;
mld = (struct mld_msg *)icmp6_hdr(skb);
- group = &mld->mld_mca;
- group_type = ipv6_addr_type(group);
+ group = mld->mld_mca;
+ group_type = ipv6_addr_type(&group);
if (group_type != IPV6_ADDR_ANY &&
!(group_type&IPV6_ADDR_MULTICAST))
@@ -1509,7 +1509,7 @@ static void __mld_query_work(struct sk_buff *skb)
}
} else {
for_each_mc_mclock(idev, ma) {
- if (!ipv6_addr_equal(group, &ma->mca_addr))
+ if (!ipv6_addr_equal(&group, &ma->mca_addr))
continue;
if (ma->mca_flags & MAF_TIMER_RUNNING) {
/* gsquery <- gsquery && mark */
--
2.54.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH net] ipv6: mcast: Fix use-after-free when processing MLD queries
2026-06-03 10:18 [PATCH net] ipv6: mcast: Fix use-after-free when processing MLD queries Ido Schimmel
@ 2026-06-03 10:54 ` Eric Dumazet
2026-06-03 11:45 ` Jiayuan Chen
1 sibling, 0 replies; 3+ messages in thread
From: Eric Dumazet @ 2026-06-03 10:54 UTC (permalink / raw)
To: Ido Schimmel; +Cc: netdev, davem, kuba, pabeni, horms, dsahern, leo
On Wed, Jun 3, 2026 at 3:19 AM Ido Schimmel <idosch@nvidia.com> wrote:
>
> When processing an MLD query, a pointer to the multicast group address
> is retrieved when initially parsing the packet. This pointer is later
> dereferenced without being reloaded despite the fact that the skb header
> might have been reallocated following the pskb_may_pull() calls, leading
> to a use-after-free [1].
>
> Fix by copying the multicast group address when the packet is initially
> parsed.
>
> [1]
> BUG: KASAN: slab-use-after-free in __mld_query_work (net/ipv6/mcast.c:1512)
> Read of size 8 at addr ffff8881154b8e90 by task kworker/4:1/118
>
> Workqueue: mld mld_query_work
> Call Trace:
> <TASK>
> dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
> print_address_description.constprop.0 (mm/kasan/report.c:378)
> print_report (mm/kasan/report.c:482)
> kasan_report (mm/kasan/report.c:595)
> __mld_query_work (net/ipv6/mcast.c:1512)
> mld_query_work (net/ipv6/mcast.c:1563)
> process_one_work (kernel/workqueue.c:3314)
> worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
> kthread (kernel/kthread.c:436)
> ret_from_fork (arch/x86/kernel/process.c:158)
> ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
> </TASK>
>
> [...]
>
> Freed by task 118:
> kasan_save_stack (mm/kasan/common.c:57)
> kasan_save_track (mm/kasan/common.c:78)
> kasan_save_free_info (mm/kasan/generic.c:584)
> __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
> kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566)
> pskb_expand_head (net/core/skbuff.c:2335)
> __pskb_pull_tail (net/core/skbuff.c:2878 (discriminator 4))
> __mld_query_work (net/ipv6/mcast.c:1495 (discriminator 1))
> mld_query_work (net/ipv6/mcast.c:1563)
> process_one_work (kernel/workqueue.c:3314)
> worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
> kthread (kernel/kthread.c:436)
> ret_from_fork (arch/x86/kernel/process.c:158)
> ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
>
> Fixes: 97300b5fdfe2 ("[MCAST] IPv6: Check packet size when process Multicast")
> Reported-by: Leo Lin <leo@depthfirst.com>
> Reviewed-by: David Ahern <dahern@nvidia.com>
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH net] ipv6: mcast: Fix use-after-free when processing MLD queries
2026-06-03 10:18 [PATCH net] ipv6: mcast: Fix use-after-free when processing MLD queries Ido Schimmel
2026-06-03 10:54 ` Eric Dumazet
@ 2026-06-03 11:45 ` Jiayuan Chen
1 sibling, 0 replies; 3+ messages in thread
From: Jiayuan Chen @ 2026-06-03 11:45 UTC (permalink / raw)
To: Ido Schimmel, netdev; +Cc: davem, kuba, pabeni, edumazet, horms, dsahern, leo
On 6/3/26 6:18 PM, Ido Schimmel wrote:
> When processing an MLD query, a pointer to the multicast group address
> is retrieved when initially parsing the packet. This pointer is later
> dereferenced without being reloaded despite the fact that the skb header
> might have been reallocated following the pskb_may_pull() calls, leading
> to a use-after-free [1].
>
> Fix by copying the multicast group address when the packet is initially
> parsed.
>
> [1]
> BUG: KASAN: slab-use-after-free in __mld_query_work (net/ipv6/mcast.c:1512)
> Read of size 8 at addr ffff8881154b8e90 by task kworker/4:1/118
>
> Workqueue: mld mld_query_work
> Call Trace:
> <TASK>
> dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
> print_address_description.constprop.0 (mm/kasan/report.c:378)
> print_report (mm/kasan/report.c:482)
> kasan_report (mm/kasan/report.c:595)
> __mld_query_work (net/ipv6/mcast.c:1512)
> mld_query_work (net/ipv6/mcast.c:1563)
> process_one_work (kernel/workqueue.c:3314)
> worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
> kthread (kernel/kthread.c:436)
> ret_from_fork (arch/x86/kernel/process.c:158)
> ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
> </TASK>
>
> [...]
>
> Freed by task 118:
> kasan_save_stack (mm/kasan/common.c:57)
> kasan_save_track (mm/kasan/common.c:78)
> kasan_save_free_info (mm/kasan/generic.c:584)
> __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
> kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6251 mm/slub.c:6566)
> pskb_expand_head (net/core/skbuff.c:2335)
> __pskb_pull_tail (net/core/skbuff.c:2878 (discriminator 4))
> __mld_query_work (net/ipv6/mcast.c:1495 (discriminator 1))
> mld_query_work (net/ipv6/mcast.c:1563)
> process_one_work (kernel/workqueue.c:3314)
> worker_thread (kernel/workqueue.c:3397 kernel/workqueue.c:3478)
> kthread (kernel/kthread.c:436)
> ret_from_fork (arch/x86/kernel/process.c:158)
> ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
>
> Fixes: 97300b5fdfe2 ("[MCAST] IPv6: Check packet size when process Multicast")
> Reported-by: Leo Lin <leo@depthfirst.com>
> Reviewed-by: David Ahern <dahern@nvidia.com>
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-06-03 10:18 [PATCH net] ipv6: mcast: Fix use-after-free when processing MLD queries Ido Schimmel
2026-06-03 10:54 ` Eric Dumazet
2026-06-03 11:45 ` Jiayuan Chen
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