From 5353ed8deedee9e5acb9f896e9032158f5d998de Mon Sep 17 00:00:00 2001 From: Colin Ian King Date: Mon, 20 Jun 2016 15:40:27 +0100 Subject: [PATCH] devpts: fix null pointer dereference on failed memory allocation An ENOMEM when creating a pair tty in tty_ldisc_setup causes a null pointer dereference in devpts_kill_index because tty->link->driver_data is NULL. The oops was triggered with the pty stressor in stress-ng when in a low memory condition. tty_init_dev tries to clean up a tty_ldisc_setup ENOMEM error by calling release_tty, however, this ultimately tries to clean up the NULL pair'd tty in pty_unix98_remove, triggering the Oops. Add check to pty_unix98_remove to only clean up fsi if it is not NULL. Ooops: [ 23.020961] Oops: 0000 [#1] SMP [ 23.020976] Modules linked in: ppdev snd_hda_codec_generic snd_hda_intel snd_hda_codec parport_pc snd_hda_core snd_hwdep parport snd_pcm input_leds joydev snd_timer serio_raw snd soundcore i2c_piix4 mac_hid ib_iser rdma_cm iw_cm ib_cm ib_core configfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi autofs4 btrfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel qxl aes_x86_64 ttm lrw gf128mul glue_helper ablk_helper drm_kms_helper cryptd syscopyarea sysfillrect psmouse sysimgblt floppy fb_sys_fops drm pata_acpi jitterentropy_rng drbg ansi_cprng [ 23.020978] CPU: 0 PID: 1452 Comm: stress-ng-pty Not tainted 4.7.0-rc4+ #2 [ 23.020978] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 [ 23.020979] task: ffff88007ba30000 ti: ffff880078ea8000 task.ti: ffff880078ea8000 [ 23.020981] RIP: 0010:[] [] ida_remove+0x1f/0x120 [ 23.020981] RSP: 0018:ffff880078eabb60 EFLAGS: 00010a03 [ 23.020982] RAX: 4444444444444567 RBX: 0000000000000000 RCX: 000000000000001f [ 23.020982] RDX: 000000000000014c RSI: 000000000000026f RDI: 0000000000000000 [ 23.020982] RBP: ffff880078eabb70 R08: 0000000000000004 R09: 0000000000000036 [ 23.020983] R10: 000000000000026f R11: 0000000000000000 R12: 000000000000026f [ 23.020983] R13: 000000000000026f R14: ffff88007c944b40 R15: 000000000000026f [ 23.020984] FS: 00007f9a2f3cc700(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000 [ 23.020984] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 23.020985] CR2: 0000000000000010 CR3: 000000006c81b000 CR4: 00000000001406f0 [ 23.020988] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 23.020988] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 23.020988] Stack: [ 23.020989] 0000000000000000 000000000000026f ffff880078eabb90 ffffffff812a5a99 [ 23.020990] 0000000000000000 00000000fffffff4 ffff880078eabba8 ffffffff814f9cbe [ 23.020991] ffff88007965c800 ffff880078eabbc8 ffffffff814eef43 fffffffffffffff4 [ 23.020991] Call Trace: [ 23.021000] [] devpts_kill_index+0x29/0x50 [ 23.021002] [] pty_unix98_remove+0x2e/0x50 [ 23.021006] [] release_tty+0xb3/0x1b0 [ 23.021007] [] tty_init_dev+0xd4/0x1c0 [ 23.021011] [] ptmx_open+0xae/0x190 [ 23.021013] [] chrdev_open+0xbf/0x1b0 [ 23.021015] [] do_dentry_open+0x203/0x310 [ 23.021016] [] ? cdev_put+0x30/0x30 [ 23.021017] [] vfs_open+0x54/0x80 [ 23.021018] [] ? may_open+0x8c/0x100 [ 23.021019] [] path_openat+0x2eb/0x1440 [ 23.021020] [] ? putname+0x54/0x60 [ 23.021022] [] ? n_tty_ioctl_helper+0x27/0x100 [ 23.021023] [] do_filp_open+0x91/0x100 [ 23.021024] [] ? getname_flags+0x56/0x1f0 [ 23.021026] [] ? __alloc_fd+0x46/0x190 [ 23.021027] [] do_sys_open+0x124/0x210 [ 23.021028] [] SyS_open+0x1e/0x20 [ 23.021035] [] entry_SYSCALL_64_fastpath+0x1e/0xa8 [ 23.021044] Code: 63 28 45 31 e4 eb dd 0f 1f 44 00 00 55 4c 63 d6 48 ba 89 88 88 88 88 88 88 88 4c 89 d0 b9 1f 00 00 00 48 f7 e2 48 89 e5 41 54 53 <8b> 47 10 48 89 fb 8d 3c c5 00 00 00 00 48 c1 ea 09 b8 01 00 00 [ 23.021045] RIP [] ida_remove+0x1f/0x120 [ 23.021045] RSP [ 23.021046] CR2: 0000000000000010 Signed-off-by: Colin Ian King Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/pty.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index f856c4544eea..51e0d32883ba 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -667,8 +667,11 @@ static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty) fsi = tty->driver_data; else fsi = tty->link->driver_data; - devpts_kill_index(fsi, tty->index); - devpts_release(fsi); + + if (fsi) { + devpts_kill_index(fsi, tty->index); + devpts_release(fsi); + } } static const struct tty_operations ptm_unix98_ops = { -- 2.20.1