1 files changed, 65 insertions, 51 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index a09e077ba925..2a930a752a78 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;
 		}
@@ -381,29 +392,31 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
 }
 
 static int
-checkSMBhdr(struct smb_hdr *smb, __u16 mid)
+check_smb_hdr(struct smb_hdr *smb, __u16 mid)
 {
-	/* Make sure that this really is an SMB, that it is a response,
-	   and that the message ids match */
-	if ((*(__le32 *) smb->Protocol == cpu_to_le32(0x424d53ff)) &&
-		(mid == smb->Mid)) {
-		if (smb->Flags & SMBFLG_RESPONSE)
-			return 0;
-		else {
-		/* only one valid case where server sends us request */
-			if (smb->Command == SMB_COM_LOCKING_ANDX)
-				return 0;
-			else
-				cERROR(1, "Received Request not response");
-		}
-	} else { /* bad signature or mid */
-		if (*(__le32 *) smb->Protocol != cpu_to_le32(0x424d53ff))
-			cERROR(1, "Bad protocol string signature header %x",
-				*(unsigned int *) smb->Protocol);
-		if (mid != smb->Mid)
-			cERROR(1, "Mids do not match");
+	/* does it have the right SMB "signature" ? */
+	if (*(__le32 *) smb->Protocol != cpu_to_le32(0x424d53ff)) {
+		cERROR(1, "Bad protocol string signature header 0x%x",
+			*(unsigned int *)smb->Protocol);
+		return 1;
+	}
+
+	/* Make sure that message ids match */
+	if (mid != smb->Mid) {
+		cERROR(1, "Mids do not match. received=%u expected=%u",
+			smb->Mid, mid);
+		return 1;
 	}
-	cERROR(1, "bad smb detected. The Mid=%d", smb->Mid);
+
+	/* if it's a response then accept */
+	if (smb->Flags & SMBFLG_RESPONSE)
+		return 0;
+
+	/* only one valid case where server sends us request */
+	if (smb->Command == SMB_COM_LOCKING_ANDX)
+		return 0;
+
+	cERROR(1, "Server sent request, not response. mid=%u", smb->Mid);
 	return 1;
 }
 
@@ -448,7 +461,7 @@ checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length)
 		return 1;
 	}
 
-	if (checkSMBhdr(smb, mid))
+	if (check_smb_hdr(smb, mid))
 		return 1;
 	clc_len = smbCalcSize_LE(smb);
 
@@ -465,25 +478,26 @@ checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length)
 			if (((4 + len) & 0xFFFF) == (clc_len & 0xFFFF))
 				return 0; /* bcc wrapped */
 		}
-		cFYI(1, "Calculated size %d vs length %d mismatch for mid %d",
+		cFYI(1, "Calculated size %u vs length %u mismatch for mid=%u",
 				clc_len, 4 + len, smb->Mid);
-		/* Windows XP can return a few bytes too much, presumably
-		an illegal pad, at the end of byte range lock responses
-		so we allow for that three byte pad, as long as actual
-		received length is as long or longer than calculated length */
-		/* We have now had to extend this more, since there is a
-		case in which it needs to be bigger still to handle a
-		malformed response to transact2 findfirst from WinXP when
-		access denied is returned and thus bcc and wct are zero
-		but server says length is 0x21 bytes too long as if the server
-		forget to reset the smb rfc1001 length when it reset the
-		wct and bcc to minimum size and drop the t2 parms and data */
-		if ((4+len > clc_len) && (len <= clc_len + 512))
-			return 0;
-		else {
-			cERROR(1, "RFC1001 size %d bigger than SMB for Mid=%d",
+
+		if (4 + len < clc_len) {
+			cERROR(1, "RFC1001 size %u smaller than SMB for mid=%u",
 					len, smb->Mid);
 			return 1;
+		} else if (len > clc_len + 512) {
+			/*
+			 * Some servers (Windows XP in particular) send more
+			 * data than the lengths in the SMB packet would
+			 * indicate on certain calls (byte range locks and
+			 * trans2 find first calls in particular). While the
+			 * client can handle such a frame by ignoring the
+			 * trailing data, we choose limit the amount of extra
+			 * data to 512 bytes.
+			 */
+			cERROR(1, "RFC1001 size %u more than 512 bytes larger "
+				  "than SMB for mid=%u", len, smb->Mid);
+			return 1;
 		}
 	}
 	return 0;