Currently, we allow the pending_mid_q to grow without bound with SIGKILL'ed processes. This could eventually be a DoS'able problem. An unprivileged user could a process that does a long-running call and then SIGKILL it.
If he can also intercept the NT_CANCEL calls or the replies from the server, then the pending_mid_q could grow very large, possibly even to 2^16 entries which might leave GetNextMid in an infinite loop. Fix this by imposing a hard limit of 32k calls per server. If we cross that limit, set the tcpStatus to CifsNeedReconnect to force cifsd to eventually reconnect the socket and clean out the pending_mid_q. While we're at it, clean up the function a bit and eliminate an unnecessary NULL pointer check. Signed-off-by: Jeff Layton <[email protected]> --- fs/cifs/misc.c | 37 ++++++++++++++++++++++++------------- 1 files changed, 24 insertions(+), 13 deletions(-) diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c index 77dc732..2a930a7 100644 --- a/fs/cifs/misc.c +++ b/fs/cifs/misc.c @@ -236,10 +236,7 @@ __u16 GetNextMid(struct TCP_Server_Info *server) { __u16 mid = 0; __u16 last_mid; - int collision; - - if (server == NULL) - return mid; + bool collision; spin_lock(&GlobalMid_Lock); last_mid = server->CurrentMid; /* we do not want to loop forever */ @@ -252,24 +249,38 @@ __u16 GetNextMid(struct TCP_Server_Info *server) (and it would also have to have been a request that did not time out) */ while (server->CurrentMid != last_mid) { - struct list_head *tmp; struct mid_q_entry *mid_entry; + unsigned int num_mids; - collision = 0; + collision = false; if (server->CurrentMid == 0) server->CurrentMid++; - list_for_each(tmp, &server->pending_mid_q) { - mid_entry = list_entry(tmp, struct mid_q_entry, qhead); - - if ((mid_entry->mid == server->CurrentMid) && - (mid_entry->midState == MID_REQUEST_SUBMITTED)) { + num_mids = 0; + list_for_each_entry(mid_entry, &server->pending_mid_q, qhead) { + ++num_mids; + if (mid_entry->mid == server->CurrentMid && + mid_entry->midState == MID_REQUEST_SUBMITTED) { /* This mid is in use, try a different one */ - collision = 1; + collision = true; break; } } - if (collision == 0) { + + /* + * 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 = server->CurrentMid; break; } -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
