On Thu, Feb 13, 2020 at 08:09:31AM +0100, Jiri Slaby wrote: > On 12. 02. 20, 20:59, Greg KH wrote: > > 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? > > Not necessarily -- the patches fix two different bugs (endless loop in > kernel vs crash). If you want to apply them in the opposite order, just > let me know. > > BTW I completely forgot to add Fixes and Cc: stable tags. Both of the > issues come from 1.x times. (But the crash obviously needs > SMP/preemption, i.e. 2.x.*.) No worries, I'll go add cc: stable to them now, thanks. greg k-h
