tls: device: fix out-of-bounds write in tls_append_frag()

Found with syzkaller and a local syzbot instance running on top of a netdevsim TLS offload emulation; tls_device.c is otherwise only reachable on a machine with a NIC that implements the offload.

tls_push_data() only checks whether the open record still has room for another frag at the bottom of its loop, and the MSG_MORE early break skips that check. The record survives to the next syscall with the frag count it already had, and tls_append_frag() does not check either, so with TLS_TX_ZEROCOPY_RO every splice(SPLICE_F_MORE) of a byte or two adds a non-coalescing pipe page and num_frags walks off the end of tls_record_info.frags[MAX_SKB_FRAGS]. Once the record is pushed, tls_push_record() runs the same index over sg_tx_data[MAX_SKB_FRAGS] and the sg_set_page() writes land on the destruct_work that follows it, which the workqueue then calls.

The byte limit is fine because copy drops to 0 and the loop falls through to the same check; the frag count has no such feedback.

Push the record rather than keep a full one open, which is what a plain TCP socket does - tcp_sendmsg_locked() uses tcp_mark_push() and new_segment in both the copy and the MSG_SPLICE_PAGES paths, and tls_sw already sets full_record when the sk_msg ring fills up, MSG_MORE or not.

  BUG: KASAN: slab-out-of-bounds in tls_append_frag ( net/tls/tls_device.c:269)
  Write of size 8 at addr ffff8881104d1530 by task tls_oob/450

  CPU: 2 UID: 0 PID: 450 Comm: tls_oob Not tainted 7.2.0-rc7+ #329 PREEMPT
  Call Trace:
   <TASK>
   dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
   print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
   kasan_report (mm/kasan/report.c:595)
   tls_append_frag (net/tls/tls_device.c:269)
   tls_push_data (net/tls/tls_device.c:518)
   tls_device_sendmsg (net/tls/tls_device.c:583)
   inet_sendmsg (net/ipv4/af_inet.c:865)
   sock_sendmsg (net/socket.c:775 net/socket.c:790 net/socket.c:813)
   splice_to_socket (fs/splice.c:884)
   do_splice (fs/splice.c:936 fs/splice.c:1349)
   __do_splice (fs/splice.c:1431)
   __x64_sys_splice (fs/splice.c:1634 fs/splice.c:1616)
   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:121)
   </TASK>

and, once the record is pushed:

  UBSAN: array-index-out-of-bounds in net/tls/tls_device.c:300:24
  index 18 is out of range for type 'skb_frag_t [17]'
  UBSAN: array-index-out-of-bounds in net/tls/tls_device.c:301:41
  index 18 is out of range for type 'scatterlist [17]'
  UBSAN: array-index-out-of-bounds in net/tls/tls_device.c:302:39
  index 18 is out of range for type 'scatterlist [17]'
  UBSAN: array-index-out-of-bounds in net/tls/tls_device.c:307:38
  index 26 is out of range for type 'scatterlist [17]'

kernel tried to execute NX-protected page - exploit attempt? (uid: 0)

  BUG: unable to handle page fault for address: ffffea000411a680
  #PF: supervisor instruction fetch in kernel mode
  #PF: error_code(0x0011) - permissions violation
  Oops: Oops: 0011 [#1] SMP KASAN PTI
  Workqueue: ktls_device_destruct 0xffffea000411a680
  RIP: 0010:0xffffea000411a680
  Call Trace:
   <TASK>
   worker_thread (kernel/workqueue.c:3405 kernel/workqueue.c:3486)
   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>

Fixes e8f69799810c ("net/tls: Add generic NIC offload infrastructure")

Cc [email protected]

Signed-off-by Jiayuan Chen <[email protected]>

---
Hope to get capture attention

netdevsim + tls (revised a lot locally):
https://lore.kernel.org/netdev/[email protected]/

On 8/23/26 10:47 AM, Jiayuan Chen wrote:

Quoted 9 lines

Fixes e8f69799810c ("net/tls: Add generic NIC offload infrastructure")

Cc [email protected]

Signed-off-by Jiayuan Chen <[email protected]>

---
Hope to get capture attention

netdevsim + tls (revised a lot locally):
https://lore.kernel.org/netdev/[email protected]/

I must admit that RFC series have low chances of getting full attention these days, due to constant flood situation.

Could you please re-submit that series formally?

Thanks,

Paolo