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cifs: use the expiry output of dns_query to schedule next resolution

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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>
This commit is contained in:
Shyam Prasad N 2021-05-18 15:05:50 +00:00 committed by Steve French
parent e73f0f0ee7
commit 506c1da44f
6 changed files with 65 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/cifs/cifs_dfs_ref.c
View File

@ -176,7 +176,7 @@ char *cifs_compose_mount_options(const char *sb_mountdata,
}
}
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);

4
fs/cifs/cifsglob.h
View File

@ -75,6 +75,9 @@
#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
@ -646,6 +649,7 @@ 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 */

55
fs/cifs/connect.c
View File

@ -78,6 +78,8 @@ static int reconn_set_ipaddr_from_hostname(struct TCP_Server_Info *server)
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;
@ -91,13 +93,13 @@ static int reconn_set_ipaddr_from_hostname(struct TCP_Server_Info *server)
}
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);
@ -106,7 +108,45 @@ static int reconn_set_ipaddr_from_hostname(struct TCP_Server_Info *server)
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
@ -680,6 +720,7 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
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;
@ -1260,6 +1301,7 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
spin_unlock(&cifs_tcp_ses_lock);
cancel_delayed_work_sync(&server->echo);
cancel_delayed_work_sync(&server->resolve);
if (from_reconnect)
/*
@ -1342,6 +1384,7 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx)
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,
@ -1427,6 +1470,12 @@ 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:

10
fs/cifs/dns_resolve.c
View File

@ -24,6 +24,7 @@
* 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.
@ -31,7 +32,7 @@
* 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;
@ -66,13 +67,14 @@ dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
/* 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:

2
fs/cifs/dns_resolve.h
View File

@ -12,7 +12,7 @@
#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 */

2
fs/cifs/misc.c
View File

@ -1187,7 +1187,7 @@ int match_target_ip(struct TCP_Server_Info *server,
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;