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authorPeter Hurley <peter@hurleysoftware.com>2015-11-27 14:30:21 -0500
committerWinnie Hsu <whsu@nvidia.com>2018-04-19 10:57:47 -0700
commit1de99ac66623dc420140c8a1a6c0271a553fe515 (patch)
treed3e41952fe0abeba03078987b27273fc67171d63
parentba7727c3c66d5bd035ed8df69c74a613a6a7f9da (diff)
tty: Prevent ldisc drivers from re-using stale tty fields
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 fd98e9419d8d622a4de91f76b306af6aa627aa9c 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) Bug 1823317 Bug 1935735 Change-Id: Ica54faa9334c587594cc19bc9da007340fda672d Cc: Tilman Schmidt <tilman@imap.cc> Cc: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Gagan Grover <ggrover@nvidia.com> Reviewed-on: http://git-master/r/1259925 (cherry picked from commit 2b1401855a2bdd31556a93feba50dd0dc0bb70e8) Reviewed-on: https://git-master.nvidia.com/r/1690300 GVS: Gerrit_Virtual_Submit Reviewed-by: Bibek Basu <bbasu@nvidia.com> Tested-by: Amulya Yarlagadda <ayarlagadda@nvidia.com> Reviewed-by: Winnie Hsu <whsu@nvidia.com>
-rw-r--r--drivers/tty/tty_ldisc.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 1afe192bef6a..b5cbe12e2815 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -400,6 +400,10 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush);
* they are not on hot paths so a little discipline won't do
* any harm.
*
+ * The line discipline-related tty_struct fields are reset to
+ * prevent the ldisc driver from re-using stale information for
+ * the new ldisc instance.
+ *
* Locking: takes termios_mutex
*/
@@ -408,6 +412,9 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
mutex_lock(&tty->termios_mutex);
tty->termios.c_line = num;
mutex_unlock(&tty->termios_mutex);
+
+ tty->disc_data = NULL;
+ tty->receive_room = 0;
}
/**