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CIFS: Fix retry mid list corruption on reconnects 

When the client hits reconnect it iterates over the mid
pending queue marking entries for retry and moving them
to a temporary list to issue callbacks later without holding
GlobalMid_Lock. In the same time there is no guarantee that
mids can't be removed from the temporary list or even
freed completely by another thread. It may cause a temporary
list corruption:

[  430.454897] list_del corruption. prev->next should be ffff98d3a8f316c0, but was 2e885cb266355469
[  430.464668] ------------[ cut here ]------------
[  430.466569] kernel BUG at lib/list_debug.c:51!
[  430.468476] invalid opcode: 0000 [#1] SMP PTI
[  430.470286] CPU: 0 PID: 13267 Comm: cifsd Kdump: loaded Not tainted 5.4.0-rc3+ #19
[  430.473472] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[  430.475872] RIP: 0010:__list_del_entry_valid.cold+0x31/0x55
...
[  430.510426] Call Trace:
[  430.511500]  cifs_reconnect+0x25e/0x610 [cifs]
[  430.513350]  cifs_readv_from_socket+0x220/0x250 [cifs]
[  430.515464]  cifs_read_from_socket+0x4a/0x70 [cifs]
[  430.517452]  ? try_to_wake_up+0x212/0x650
[  430.519122]  ? cifs_small_buf_get+0x16/0x30 [cifs]
[  430.521086]  ? allocate_buffers+0x66/0x120 [cifs]
[  430.523019]  cifs_demultiplex_thread+0xdc/0xc30 [cifs]
[  430.525116]  kthread+0xfb/0x130
[  430.526421]  ? cifs_handle_standard+0x190/0x190 [cifs]
[  430.528514]  ? kthread_park+0x90/0x90
[  430.530019]  ret_from_fork+0x35/0x40

Fix this by obtaining extra references for mids being retried
and marking them as MID_DELETED which indicates that such a mid
has been dequeued from the pending list.

Also move mid cleanup logic from DeleteMidQEntry to
_cifs_mid_q_entry_release which is called when the last reference
to a particular mid is put. This allows to avoid any use-after-free
of response buffers.

The patch needs to be backported to stable kernels. A stable tag
is not mentioned below because the patch doesn't apply cleanly
to any actively maintained stable kernel.

Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-and-tested-by: David Wysochanski <dwysocha@redhat.com>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Pavel Shilovsky 2019-10-22 08:41:42 -07:00 committed by Steve French
parent 783bf7b8b6
commit abe57073d0
2 changed files with 32 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/cifs/connect.c
View File

@ -564,9 +564,11 @@ cifs_reconnect(struct TCP_Server_Info *server)
spin_lock(&GlobalMid_Lock);
list_for_each_safe(tmp, tmp2, &server->pending_mid_q) {
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
kref_get(&mid_entry->refcount);
if (mid_entry->mid_state == MID_REQUEST_SUBMITTED)
mid_entry->mid_state = MID_RETRY_NEEDED;
list_move(&mid_entry->qhead, &retry_list);
mid_entry->mid_flags |= MID_DELETED;
}
spin_unlock(&GlobalMid_Lock);
mutex_unlock(&server->srv_mutex);
@ -576,6 +578,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
list_del_init(&mid_entry->qhead);
mid_entry->callback(mid_entry);
cifs_mid_q_entry_release(mid_entry);
}
if (cifs_rdma_enabled(server)) {
@ -895,8 +898,10 @@ dequeue_mid(struct mid_q_entry *mid, bool malformed)
if (mid->mid_flags & MID_DELETED)
printk_once(KERN_WARNING
"trying to dequeue a deleted mid\n");
else
else {
list_del_init(&mid->qhead);
mid->mid_flags |= MID_DELETED;
}
spin_unlock(&GlobalMid_Lock);
}
@ -966,8 +971,10 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
list_for_each_safe(tmp, tmp2, &server->pending_mid_q) {
mid_entry = list_entry(tmp, struct mid_q_entry, qhead);
cifs_dbg(FYI, "Clearing mid 0x%llx\n", mid_entry->mid);
kref_get(&mid_entry->refcount);
mid_entry->mid_state = MID_SHUTDOWN;
list_move(&mid_entry->qhead, &dispose_list);
mid_entry->mid_flags |= MID_DELETED;
}
spin_unlock(&GlobalMid_Lock);
@ -977,6 +984,7 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
cifs_dbg(FYI, "Callback mid 0x%llx\n", mid_entry->mid);
list_del_init(&mid_entry->qhead);
mid_entry->callback(mid_entry);
cifs_mid_q_entry_release(mid_entry);
}
/* 1/8th of sec is more than enough time for them to exit */
msleep(125);

42
fs/cifs/transport.c
View File

@ -86,22 +86,8 @@ AllocMidQEntry(const struct smb_hdr *smb_buffer, struct TCP_Server_Info *server)
static void _cifs_mid_q_entry_release(struct kref *refcount)
{
struct mid_q_entry *mid = container_of(refcount, struct mid_q_entry,
refcount);
mempool_free(mid, cifs_mid_poolp);
}
void cifs_mid_q_entry_release(struct mid_q_entry *midEntry)
{
spin_lock(&GlobalMid_Lock);
kref_put(&midEntry->refcount, _cifs_mid_q_entry_release);
spin_unlock(&GlobalMid_Lock);
}
void
DeleteMidQEntry(struct mid_q_entry *midEntry)
{
struct mid_q_entry *midEntry =
container_of(refcount, struct mid_q_entry, refcount);
#ifdef CONFIG_CIFS_STATS2
__le16 command = midEntry->server->vals->lock_cmd;
__u16 smb_cmd = le16_to_cpu(midEntry->command);
@ -166,6 +152,19 @@ DeleteMidQEntry(struct mid_q_entry *midEntry)
}
}
#endif
mempool_free(midEntry, cifs_mid_poolp);
}
void cifs_mid_q_entry_release(struct mid_q_entry *midEntry)
{
spin_lock(&GlobalMid_Lock);
kref_put(&midEntry->refcount, _cifs_mid_q_entry_release);
spin_unlock(&GlobalMid_Lock);
}
void DeleteMidQEntry(struct mid_q_entry *midEntry)
{
cifs_mid_q_entry_release(midEntry);
}
@ -173,8 +172,10 @@ void
cifs_delete_mid(struct mid_q_entry *mid)
{
spin_lock(&GlobalMid_Lock);
list_del_init(&mid->qhead);
mid->mid_flags |= MID_DELETED;
if (!(mid->mid_flags & MID_DELETED)) {
list_del_init(&mid->qhead);
mid->mid_flags |= MID_DELETED;
}
spin_unlock(&GlobalMid_Lock);
DeleteMidQEntry(mid);
@ -872,7 +873,10 @@ cifs_sync_mid_result(struct mid_q_entry *mid, struct TCP_Server_Info *server)
rc = -EHOSTDOWN;
break;
default:
list_del_init(&mid->qhead);
if (!(mid->mid_flags & MID_DELETED)) {
list_del_init(&mid->qhead);
mid->mid_flags |= MID_DELETED;
}
cifs_server_dbg(VFS, "%s: invalid mid state mid=%llu state=%d\n",
__func__, mid->mid, mid->mid_state);
rc = -EIO;