On Mon, Feb 10, 2020 at 09:11:31AM +0100, Jiri Slaby wrote: > syzkaller reported this UAF: > BUG: KASAN: use-after-free in n_tty_receive_buf_common+0x2481/0x2940 drivers/tty/n_tty.c:1741 > Read of size 1 at addr ffff8880089e40e9 by task syz-executor.1/13184 > > CPU: 0 PID: 13184 Comm: syz-executor.1 Not tainted 5.4.7 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 > Call Trace: > ... > kasan_report+0xe/0x20 mm/kasan/common.c:634 > n_tty_receive_buf_common+0x2481/0x2940 drivers/tty/n_tty.c:1741 > tty_ldisc_receive_buf+0xac/0x190 drivers/tty/tty_buffer.c:461 > paste_selection+0x297/0x400 drivers/tty/vt/selection.c:372 > tioclinux+0x20d/0x4e0 drivers/tty/vt/vt.c:3044 > vt_ioctl+0x1bcf/0x28d0 drivers/tty/vt/vt_ioctl.c:364 > tty_ioctl+0x525/0x15a0 drivers/tty/tty_io.c:2657 > vfs_ioctl fs/ioctl.c:47 [inline] > > It is due to a race between parallel paste_selection (TIOCL_PASTESEL) > and set_selection_user (TIOCL_SETSEL) invocations. One uses sel_buffer, > while the other frees it and reallocates a new one for another > selection. Add a mutex to close this race. > > The mutex takes care properly of sel_buffer and sel_buffer_lth only. The > other selection global variables (like sel_start, sel_end, and sel_cons) > are protected only in set_selection_user. The other functions need quite > some more work to close the races of the variables there. This is going > to happen later. > > This likely fixes (I am unsure as there is no reproducer provided) bug > 206361 too. It was marked as CVE-2020-8648. > > Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> > Reported-by: syzbot+59997e8d5cbdc486e6f6@xxxxxxxxxxxxxxxxxxxxxxxxx > References: https://bugzilla.kernel.org/show_bug.cgi?id=206361 This needs patch 1 in order to work properly, right? thanks, greg k-h
