[PATCH 5.5 29/56] CIFS: Fix task struct use-after-free on reconnect

From: Greg Kroah-Hartman
Date: Thu Jan 30 2020 - 13:40:43 EST

From: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>

commit f1f27ad74557e39f67a8331a808b860f89254f2d upstream.

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@xxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
CC: Stable <stable@xxxxxxxxxxxxxxx>
Reviewed-by: Paulo Alcantara (SUSE) <pc@xxxxxx>
Reviewed-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/cifs/cifsglob.h | 1 +
fs/cifs/smb2transport.c | 2 ++
fs/cifs/transport.c | 3 +++
3 files changed, 6 insertions(+)

--- 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 */
--- a/fs/cifs/smb2transport.c
+++ b/fs/cifs/smb2transport.c
@@ -685,6 +685,8 @@ smb2_mid_entry_alloc(const struct smb2_s
* 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;

--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -76,6 +76,8 @@ AllocMidQEntry(const struct smb_hdr *smb
* 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(st
}
}
#endif
+ put_task_struct(midEntry->creator);

mempool_free(midEntry, cifs_mid_poolp);
}