From: Pavel Shilovsky pshilov@microsoft.com
commit abe57073d08c13b95a46ccf48cc9dc957d5c6fdb upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/cifs/connect.c | 10 +++++++++- fs/cifs/transport.c | 42 +++++++++++++++++++++++------------------- 2 files changed, 32 insertions(+), 20 deletions(-)
--- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -556,9 +556,11 @@ cifs_reconnect(struct TCP_Server_Info *s 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); @@ -568,6 +570,7 @@ cifs_reconnect(struct TCP_Server_Info *s 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)) { @@ -887,8 +890,10 @@ dequeue_mid(struct mid_q_entry *mid, boo 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); }
@@ -958,8 +963,10 @@ static void clean_demultiplex_info(struc 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);
@@ -969,6 +976,7 @@ static void clean_demultiplex_info(struc 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); --- a/fs/cifs/transport.c +++ b/fs/cifs/transport.c @@ -86,22 +86,8 @@ AllocMidQEntry(const struct smb_hdr *smb
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 *midE } } #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); @@ -868,7 +869,10 @@ cifs_sync_mid_result(struct mid_q_entry 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_dbg(VFS, "%s: invalid mid state mid=%llu state=%d\n", __func__, mid->mid, mid->mid_state); rc = -EIO;