[PATCH 5.12 001/292] cifs: use the expiry output of dns_query to schedule next resolution

Greg Kroah-Hartman
2021-07-19T17:58:43Z

From: Shyam Prasad N <sprasad@microsoft.com>

commit 506c1da44fee32ba1d3a70413289ad58c772bba6 upstream.

We recently fixed DNS resolution of the server hostname during reconnect.
However, server IP address may change, even when the old one continues
to server (although sub-optimally).

We should schedule the next DNS resolution based on the TTL of
the DNS record used for the last resolution. This way, we resolve the
server hostname again when a DNS record expires.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Cc: <stable@vger.kernel.org> # v5.11+
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/cifs/cifs_dfs_ref.c | 2 -
fs/cifs/cifsglob.h | 4 +++
fs/cifs/connect.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++---
fs/cifs/dns_resolve.c | 10 +++++---
fs/cifs/dns_resolve.h | 2 -
fs/cifs/misc.c | 2 -
6 files changed, 65 insertions(+), 10 deletions(-)

--- a/fs/cifs/cifs_dfs_ref.c
+++ b/fs/cifs/cifs_dfs_ref.c
@@ -173,7 +173,7 @@ char *cifs_compose_mount_options(const c
}
}

- rc = dns_resolve_server_name_to_ip(name, &srvIP);
+ rc = dns_resolve_server_name_to_ip(name, &srvIP, NULL);
if (rc < 0) {
cifs_dbg(FYI, "%s: Failed to resolve server part of %s to IP: %d\n",
__func__, name, rc);
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -84,6 +84,9 @@
#define SMB_ECHO_INTERVAL_MAX 600
#define SMB_ECHO_INTERVAL_DEFAULT 60

+/* dns resolution interval in seconds */
+#define SMB_DNS_RESOLVE_INTERVAL_DEFAULT 600
+
/* maximum number of PDUs in one compound */
#define MAX_COMPOUND 5

@@ -654,6 +657,7 @@ struct TCP_Server_Info {
/* point to the SMBD connection if RDMA is used instead of socket */
struct smbd_connection *smbd_conn;
struct delayed_work echo; /* echo ping workqueue job */
+ struct delayed_work resolve; /* dns resolution workqueue job */
char *smallbuf; /* pointer to current "small" buffer */
char *bigbuf; /* pointer to current "big" buffer */
/* Total size of this PDU. Only valid from cifs_demultiplex_thread */
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -92,6 +92,8 @@ static int reconn_set_ipaddr_from_hostna
int rc;
int len;
char *unc, *ipaddr = NULL;
+ time64_t expiry, now;
+ unsigned long ttl = SMB_DNS_RESOLVE_INTERVAL_DEFAULT;

if (!server->hostname)
return -EINVAL;
@@ -105,13 +107,13 @@ static int reconn_set_ipaddr_from_hostna
}
scnprintf(unc, len, "\\\\%s", server->hostname);

- rc = dns_resolve_server_name_to_ip(unc, &ipaddr);
+ rc = dns_resolve_server_name_to_ip(unc, &ipaddr, &expiry);
kfree(unc);

if (rc < 0) {
cifs_dbg(FYI, "%s: failed to resolve server part of %s to IP: %d\n",
__func__, server->hostname, rc);
- return rc;
+ goto requeue_resolve;
}

spin_lock(&cifs_tcp_ses_lock);
@@ -120,7 +122,45 @@ static int reconn_set_ipaddr_from_hostna
spin_unlock(&cifs_tcp_ses_lock);
kfree(ipaddr);

- return !rc ? -1 : 0;
+ /* rc == 1 means success here */
+ if (rc) {
+ now = ktime_get_real_seconds();
+ if (expiry && expiry > now)
+ /*
+ * To make sure we don't use the cached entry, retry 1s
+ * after expiry.
+ */
+ ttl = (expiry - now + 1);
+ }
+ rc = !rc ? -1 : 0;
+
+requeue_resolve:
+ cifs_dbg(FYI, "%s: next dns resolution scheduled for %lu seconds in the future\n",
+ __func__, ttl);
+ mod_delayed_work(cifsiod_wq, &server->resolve, (ttl * HZ));
+
+ return rc;
+}
+
+
+static void cifs_resolve_server(struct work_struct *work)
+{
+ int rc;
+ struct TCP_Server_Info *server = container_of(work,
+ struct TCP_Server_Info, resolve.work);
+
+ mutex_lock(&server->srv_mutex);
+
+ /*
+ * Resolve the hostname again to make sure that IP address is up-to-date.
+ */
+ rc = reconn_set_ipaddr_from_hostname(server);
+ if (rc) {
+ cifs_dbg(FYI, "%s: failed to resolve hostname: %d\n",
+ __func__, rc);
+ }
+
+ mutex_unlock(&server->srv_mutex);
}

#ifdef CONFIG_CIFS_DFS_UPCALL
@@ -720,6 +760,7 @@ static void clean_demultiplex_info(struc
spin_unlock(&cifs_tcp_ses_lock);

cancel_delayed_work_sync(&server->echo);
+ cancel_delayed_work_sync(&server->resolve);

spin_lock(&GlobalMid_Lock);
server->tcpStatus = CifsExiting;
@@ -1300,6 +1341,7 @@ cifs_put_tcp_session(struct TCP_Server_I
spin_unlock(&cifs_tcp_ses_lock);

cancel_delayed_work_sync(&server->echo);
+ cancel_delayed_work_sync(&server->resolve);

if (from_reconnect)
/*
@@ -1382,6 +1424,7 @@ cifs_get_tcp_session(struct smb3_fs_cont
INIT_LIST_HEAD(&tcp_ses->tcp_ses_list);
INIT_LIST_HEAD(&tcp_ses->smb_ses_list);
INIT_DELAYED_WORK(&tcp_ses->echo, cifs_echo_request);
+ INIT_DELAYED_WORK(&tcp_ses->resolve, cifs_resolve_server);
INIT_DELAYED_WORK(&tcp_ses->reconnect, smb2_reconnect_server);
mutex_init(&tcp_ses->reconnect_mutex);
memcpy(&tcp_ses->srcaddr, &ctx->srcaddr,
@@ -1462,6 +1505,12 @@ smbd_connected:
/* queue echo request delayed work */
queue_delayed_work(cifsiod_wq, &tcp_ses->echo, tcp_ses->echo_interval);

+ /* queue dns resolution delayed work */
+ cifs_dbg(FYI, "%s: next dns resolution scheduled for %d seconds in the future\n",
+ __func__, SMB_DNS_RESOLVE_INTERVAL_DEFAULT);
+
+ queue_delayed_work(cifsiod_wq, &tcp_ses->resolve, (SMB_DNS_RESOLVE_INTERVAL_DEFAULT * HZ));
+
return tcp_ses;

out_err_crypto_release:
--- a/fs/cifs/dns_resolve.c
+++ b/fs/cifs/dns_resolve.c
@@ -36,6 +36,7 @@
* dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
* @unc: UNC path specifying the server (with '/' as delimiter)
* @ip_addr: Where to return the IP address.
+ * @expiry: Where to return the expiry time for the dns record.
*
* The IP address will be returned in string form, and the caller is
* responsible for freeing it.
@@ -43,7 +44,7 @@
* Returns length of result on success, -ve on error.
*/
int
-dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
+dns_resolve_server_name_to_ip(const char *unc, char **ip_addr, time64_t *expiry)
{
struct sockaddr_storage ss;
const char *hostname, *sep;
@@ -78,13 +79,14 @@ dns_resolve_server_name_to_ip(const char

/* Perform the upcall */
rc = dns_query(current->nsproxy->net_ns, NULL, hostname, len,
- NULL, ip_addr, NULL, false);
+ NULL, ip_addr, expiry, false);
if (rc < 0)
cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
__func__, len, len, hostname);
else
- cifs_dbg(FYI, "%s: resolved: %*.*s to %s\n",
- __func__, len, len, hostname, *ip_addr);
+ cifs_dbg(FYI, "%s: resolved: %*.*s to %s expiry %llu\n",
+ __func__, len, len, hostname, *ip_addr,
+ expiry ? (*expiry) : 0);
return rc;

name_is_IP_address:
--- a/fs/cifs/dns_resolve.h
+++ b/fs/cifs/dns_resolve.h
@@ -24,7 +24,7 @@
#define _DNS_RESOLVE_H

#ifdef __KERNEL__
-extern int dns_resolve_server_name_to_ip(const char *unc, char **ip_addr);
+extern int dns_resolve_server_name_to_ip(const char *unc, char **ip_addr, time64_t *expiry);
#endif /* KERNEL */

#endif /* _DNS_RESOLVE_H */
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -1105,7 +1105,7 @@ int match_target_ip(struct TCP_Server_In

cifs_dbg(FYI, "%s: target name: %s\n", __func__, target + 2);

- rc = dns_resolve_server_name_to_ip(target, &tip);
+ rc = dns_resolve_server_name_to_ip(target, &tip, NULL);
if (rc < 0)
goto out;