Commit ee9159dd authored by Peter Hurley's avatar Peter Hurley Committed by David S. Miller

wan/x25: Fix use-after-free in x25_asy_open_tty()

The N_X25 line discipline may access the previous line discipline's closed
and already-freed private data on open [1].

The tty->disc_data field _never_ refers to valid data on entry to the
line discipline's open() method. Rather, the ldisc is expected to
initialize that field for its own use for the lifetime of the instance
(ie. from open() to close() only).

[1]
    [  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)
Reported-and-tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 304d888b
...@@ -549,16 +549,12 @@ static void x25_asy_receive_buf(struct tty_struct *tty, ...@@ -549,16 +549,12 @@ static void x25_asy_receive_buf(struct tty_struct *tty,
static int x25_asy_open_tty(struct tty_struct *tty) static int x25_asy_open_tty(struct tty_struct *tty)
{ {
struct x25_asy *sl = tty->disc_data; struct x25_asy *sl;
int err; int err;
if (tty->ops->write == NULL) if (tty->ops->write == NULL)
return -EOPNOTSUPP; return -EOPNOTSUPP;
/* First make sure we're not already connected. */
if (sl && sl->magic == X25_ASY_MAGIC)
return -EEXIST;
/* OK. Find a free X.25 channel to use. */ /* OK. Find a free X.25 channel to use. */
sl = x25_asy_alloc(); sl = x25_asy_alloc();
if (sl == NULL) if (sl == NULL)
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment