CVE-2026-98839

In the Linux kernel, the following vulnerability has been resolved:

vt: selection: Fix unsigned underflow and slab-out-of-bounds read in paste_selection()

In paste_selection(), the loop copies min_t(unsigned int,
vc_sel.buf_len - pasted,tty->receive_room) bytes per iteration into
tty_ldisc_receive_buf() and increments pasted += count.

Because the selection mutex (vc_sel.lock) is dropped inside the loop
Whenever the line discipline buffer fills up and paste_selection()
sleeps on tty->write_wait, a concurrent TIOCLINUX (TIOCL_SETSEL) ioctl
can replace vc_sel.buffer with a shorter selection and reduce
vc_sel.buf_len below pasted.

When paste_selection() resumes, vc_sel.buf_len - pasted underflows as an
unsigned integer to a large positive value, causing
tty_ldisc_receive_buf(ld, vc_sel.buffer + pasted, NULL, count) to read
up to 4094 bytes out-of-bounds past the newly allocated vc_sel.buffer.

Fix this by terminating the loop when pasted >= vc_sel.buf_len.

Kernel stack trace (Linux 7.3.0-rc3):
 ==================================================================
 BUG: KASAN: slab-out-of-bounds in n_tty_receive_buf_common+0xa01/0x1650
 Read of size 4094 at addr ffff888101c58010 by task kworker/u17:1/65
 Workqueue: events_unbound flush_to_ldisc
 Call Trace:
  <TASK>
  dump_stack_lvl+0x70/0xa0
  print_report+0x153/0x4c6
  kasan_report+0xf1/0x120
  kasan_check_range+0x11c/0x200
  __asan_memcpy+0x29/0x70
  n_tty_receive_buf_common+0xa01/0x1650
  tty_ldisc_receive_buf+0x66/0x110
  tty_port_default_receive_buf+0x6b/0xb0
  flush_to_ldisc+0x1b4/0x410
  process_one_work+0x6ff/0x1110
  worker_thread+0x4a8/0xb70
  kthread+0x307/0x3e0
  ret_from_fork+0x3ed/0x680
  </TASK>
 ==================================================================