diff options
Diffstat (limited to 'fs/cifs/smb1ops.c')
| -rw-r--r-- | fs/cifs/smb1ops.c | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/fs/cifs/smb1ops.c b/fs/cifs/smb1ops.c index d9d615fbed3f..6dec38f5522d 100644 --- a/fs/cifs/smb1ops.c +++ b/fs/cifs/smb1ops.c @@ -125,6 +125,94 @@ cifs_get_credits_field(struct TCP_Server_Info *server) return &server->credits; } +/* + * Find a free multiplex id (SMB mid). Otherwise there could be + * mid collisions which might cause problems, demultiplexing the + * wrong response to this request. Multiplex ids could collide if + * one of a series requests takes much longer than the others, or + * if a very large number of long lived requests (byte range + * locks or FindNotify requests) are pending. No more than + * 64K-1 requests can be outstanding at one time. If no + * mids are available, return zero. A future optimization + * could make the combination of mids and uid the key we use + * to demultiplex on (rather than mid alone). + * In addition to the above check, the cifs demultiplex + * code already used the command code as a secondary + * check of the frame and if signing is negotiated the + * response would be discarded if the mid were the same + * but the signature was wrong. Since the mid is not put in the + * pending queue until later (when it is about to be dispatched) + * we do have to limit the number of outstanding requests + * to somewhat less than 64K-1 although it is hard to imagine + * so many threads being in the vfs at one time. + */ +static __u64 +cifs_get_next_mid(struct TCP_Server_Info *server) +{ + __u64 mid = 0; + __u16 last_mid, cur_mid; + bool collision; + + spin_lock(&GlobalMid_Lock); + + /* mid is 16 bit only for CIFS/SMB */ + cur_mid = (__u16)((server->CurrentMid) & 0xffff); + /* we do not want to loop forever */ + last_mid = cur_mid; + cur_mid++; + + /* + * This nested loop looks more expensive than it is. + * In practice the list of pending requests is short, + * fewer than 50, and the mids are likely to be unique + * on the first pass through the loop unless some request + * takes longer than the 64 thousand requests before it + * (and it would also have to have been a request that + * did not time out). + */ + while (cur_mid != last_mid) { + struct mid_q_entry *mid_entry; + unsigned int num_mids; + + collision = false; + if (cur_mid == 0) + cur_mid++; + + num_mids = 0; + list_for_each_entry(mid_entry, &server->pending_mid_q, qhead) { + ++num_mids; + if (mid_entry->mid == cur_mid && + mid_entry->mid_state == MID_REQUEST_SUBMITTED) { + /* This mid is in use, try a different one */ + collision = true; + break; + } + } + + /* + * if we have more than 32k mids in the list, then something + * is very wrong. Possibly a local user is trying to DoS the + * box by issuing long-running calls and SIGKILL'ing them. If + * we get to 2^16 mids then we're in big trouble as this + * function could loop forever. + * + * Go ahead and assign out the mid in this situation, but force + * an eventual reconnect to clean out the pending_mid_q. + */ + if (num_mids > 32768) + server->tcpStatus = CifsNeedReconnect; + + if (!collision) { + mid = (__u64)cur_mid; + server->CurrentMid = mid; + break; + } + cur_mid++; + } + spin_unlock(&GlobalMid_Lock); + return mid; +} + struct smb_version_operations smb1_operations = { .send_cancel = send_nt_cancel, .compare_fids = cifs_compare_fids, @@ -133,6 +221,7 @@ struct smb_version_operations smb1_operations = { .add_credits = cifs_add_credits, .set_credits = cifs_set_credits, .get_credits_field = cifs_get_credits_field, + .get_next_mid = cifs_get_next_mid, .read_data_offset = cifs_read_data_offset, .read_data_length = cifs_read_data_length, .map_error = map_smb_to_linux_error, |
