Re: [PATCH] CIFS: Fix retry mid list corruption on reconnects

[Steve French <smfrench@gmail.com>]

tentatively merged into cifs-2.6.git for-next

running buildbot now ...
http://smb3-test-rhel-75.southcentralus.cloudapp.azure.com/#/builders/2/builds/268

On Tue, Oct 22, 2019 at 5:35 PM Pavel Shilovsky <piastryyy@gmail.com> wrote:
>
> 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>
> ---
>  fs/cifs/connect.c   | 10 +++++++++-
>  fs/cifs/transport.c | 42 +++++++++++++++++++++++-------------------
>  2 files changed, 32 insertions(+), 20 deletions(-)
>
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index b724227b853c..ac43c79ebdf5 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -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);
> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
> index 308ad0f495e1..ca3de62688d6 100644
> --- a/fs/cifs/transport.c
> +++ b/fs/cifs/transport.c
> @@ -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;
> --
> 2.17.1
>


-- 
Thanks,

Steve