The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f1f27ad74557e39f67a8331a808b860f89254f2d Mon Sep 17 00:00:00 2001

From: Vincent Whitchurch vincent.whitchurch@axis.com Date: Thu, 23 Jan 2020 17:09:06 +0100 Subject: [PATCH] CIFS: Fix task struct use-after-free on reconnect

The task which created the MID may be gone by the time cifsd attempts to call the callbacks on MIDs from cifs_reconnect().

This leads to a use-after-free of the task struct in cifs_wake_up_task:

================================================================== BUG: KASAN: use-after-free in __lock_acquire+0x31a0/0x3270 Read of size 8 at addr ffff8880103e3a68 by task cifsd/630

CPU: 0 PID: 630 Comm: cifsd Not tainted 5.5.0-rc6+ #119 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 Call Trace: dump_stack+0x8e/0xcb print_address_description.constprop.5+0x1d3/0x3c0 ? __lock_acquire+0x31a0/0x3270 __kasan_report+0x152/0x1aa ? __lock_acquire+0x31a0/0x3270 ? __lock_acquire+0x31a0/0x3270 kasan_report+0xe/0x20 __lock_acquire+0x31a0/0x3270 ? __wake_up_common+0x1dc/0x630 ? _raw_spin_unlock_irqrestore+0x4c/0x60 ? mark_held_locks+0xf0/0xf0 ? _raw_spin_unlock_irqrestore+0x39/0x60 ? __wake_up_common_lock+0xd5/0x130 ? __wake_up_common+0x630/0x630 lock_acquire+0x13f/0x330 ? try_to_wake_up+0xa3/0x19e0 _raw_spin_lock_irqsave+0x38/0x50 ? try_to_wake_up+0xa3/0x19e0 try_to_wake_up+0xa3/0x19e0 ? cifs_compound_callback+0x178/0x210 ? set_cpus_allowed_ptr+0x10/0x10 cifs_reconnect+0xa1c/0x15d0 ? generic_ip_connect+0x1860/0x1860 ? rwlock_bug.part.0+0x90/0x90 cifs_readv_from_socket+0x479/0x690 cifs_read_from_socket+0x9d/0xe0 ? cifs_readv_from_socket+0x690/0x690 ? mempool_resize+0x690/0x690 ? rwlock_bug.part.0+0x90/0x90 ? memset+0x1f/0x40 ? allocate_buffers+0xff/0x340 cifs_demultiplex_thread+0x388/0x2a50 ? cifs_handle_standard+0x610/0x610 ? rcu_read_lock_held_common+0x120/0x120 ? mark_lock+0x11b/0xc00 ? __lock_acquire+0x14ed/0x3270 ? __kthread_parkme+0x78/0x100 ? lockdep_hardirqs_on+0x3e8/0x560 ? lock_downgrade+0x6a0/0x6a0 ? lockdep_hardirqs_on+0x3e8/0x560 ? _raw_spin_unlock_irqrestore+0x39/0x60 ? cifs_handle_standard+0x610/0x610 kthread+0x2bb/0x3a0 ? kthread_create_worker_on_cpu+0xc0/0xc0 ret_from_fork+0x3a/0x50

Allocated by task 649: save_stack+0x19/0x70 __kasan_kmalloc.constprop.5+0xa6/0xf0 kmem_cache_alloc+0x107/0x320 copy_process+0x17bc/0x5370 _do_fork+0x103/0xbf0 __x64_sys_clone+0x168/0x1e0 do_syscall_64+0x9b/0xec0 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0: save_stack+0x19/0x70 __kasan_slab_free+0x11d/0x160 kmem_cache_free+0xb5/0x3d0 rcu_core+0x52f/0x1230 __do_softirq+0x24d/0x962

The buggy address belongs to the object at ffff8880103e32c0 which belongs to the cache task_struct of size 6016 The buggy address is located 1960 bytes inside of 6016-byte region [ffff8880103e32c0, ffff8880103e4a40) The buggy address belongs to the page: page:ffffea000040f800 refcount:1 mapcount:0 mapping:ffff8880108da5c0 index:0xffff8880103e4c00 compound_mapcount: 0 raw: 4000000000010200 ffffea00001f2208 ffffea00001e3408 ffff8880108da5c0 raw: ffff8880103e4c00 0000000000050003 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff8880103e3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880103e3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

ffff8880103e3a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

^ ffff8880103e3a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880103e3b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================

This can be reliably reproduced by adding the below delay to cifs_reconnect(), running find(1) on the mount, restarting the samba server while find is running, and killing find during the delay:

spin_unlock(&GlobalMid_Lock); mutex_unlock(&server->srv_mutex);

+ msleep(10000); + cifs_dbg(FYI, "%s: issuing mid callbacks\n", __func__); list_for_each_safe(tmp, tmp2, &retry_list) { mid_entry = list_entry(tmp, struct mid_q_entry, qhead);

Fix this by holding a reference to the task struct until the MID is freed.

Signed-off-by: Vincent Whitchurch vincent.whitchurch@axis.com Signed-off-by: Steve French stfrench@microsoft.com CC: Stable stable@vger.kernel.org Reviewed-by: Paulo Alcantara (SUSE) pc@cjr.nz Reviewed-by: Pavel Shilovsky pshilov@microsoft.com

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h index 40705e862451..239338d57086 100644 --- a/fs/cifs/cifsglob.h +++ b/fs/cifs/cifsglob.h @@ -1588,6 +1588,7 @@ struct mid_q_entry { mid_callback_t *callback; /* call completion callback */ mid_handle_t *handle; /* call handle mid callback */ void *callback_data; /* general purpose pointer for callback */ + struct task_struct *creator; void *resp_buf; /* pointer to received SMB header */ unsigned int resp_buf_size; int mid_state; /* wish this were enum but can not pass to wait_event */ diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c index 387c88704c52..fe6acfce3390 100644 --- a/fs/cifs/smb2transport.c +++ b/fs/cifs/smb2transport.c @@ -685,6 +685,8 @@ smb2_mid_entry_alloc(const struct smb2_sync_hdr *shdr, * The default is for the mid to be synchronous, so the * default callback just wakes up the current task. */ + get_task_struct(current); + temp->creator = current; temp->callback = cifs_wake_up_task; temp->callback_data = current;

diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c index 3d2e11f85cba..cb3ee916f527 100644 --- a/fs/cifs/transport.c +++ b/fs/cifs/transport.c @@ -76,6 +76,8 @@ AllocMidQEntry(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server) * The default is for the mid to be synchronous, so the * default callback just wakes up the current task. */ + get_task_struct(current); + temp->creator = current; temp->callback = cifs_wake_up_task; temp->callback_data = current;

@@ -158,6 +160,7 @@ static void _cifs_mid_q_entry_release(struct kref *refcount) } } #endif + put_task_struct(midEntry->creator);

mempool_free(midEntry, cifs_mid_poolp); }