• Peter Hurley's avatar
    tty: Prevent ldisc drivers from re-using stale tty fields · f98d8917
    Peter Hurley authored
    commit dd42bf11 upstream.
    
    Line discipline drivers may mistakenly misuse ldisc-related fields
    when initializing. For example, a failure to initialize tty->receive_room
    in the N_GIGASET_M101 line discipline was recently found and fixed [1].
    Now, the N_X25 line discipline has been discovered accessing the previous
    line discipline's already-freed private data [2].
    
    Harden the ldisc interface against misuse by initializing revelant
    tty fields before instancing the new line discipline.
    
    [1]
        commit fd98e941
        Author: Tilman Schmidt <tilman@imap.cc>
        Date:   Tue Jul 14 00:37:13 2015 +0200
    
        isdn/gigaset: reset tty->receive_room when attaching ser_gigaset
    
    [2] Report from Sasha Levin <sasha.levin@oracle.com>
        [  634.336761] ==================================================================
        [  634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0
        [  634.339558] Read of size 4 by task syzkaller_execu/8981
        [  634.340359] =============================================================================
        [  634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected
        ...
        [  634.405018] Call Trace:
        [  634.405277] dump_stack (lib/dump_stack.c:52)
        [  634.405775] print_trailer (mm/slub.c:655)
        [  634.406361] object_err (mm/slub.c:662)
        [  634.406824] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236)
        [  634.409581] __asan_report_load4_noabort (mm/kasan/report.c:279)
        [  634.411355] x25_asy_open_tty (drivers/net/wan/x25_asy.c:559 (discriminator 1))
        [  634.413997] tty_ldisc_open.isra.2 (drivers/tty/tty_ldisc.c:447)
        [  634.414549] tty_set_ldisc (drivers/tty/tty_ldisc.c:567)
        [  634.415057] tty_ioctl (drivers/tty/tty_io.c:2646 drivers/tty/tty_io.c:2879)
        [  634.423524] do_vfs_ioctl (fs/ioctl.c:43 fs/ioctl.c:607)
        [  634.427491] SyS_ioctl (fs/ioctl.c:622 fs/ioctl.c:613)
        [  634.427945] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188)
    
    Cc: Tilman Schmidt <tilman@imap.cc>
    Cc: Sasha Levin <sasha.levin@oracle.com>
    Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
    Signed-off-by: default avatarAmit Pundir <amit.pundir@linaro.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    f98d8917
tty_ldisc.c 19.5 KB