From: Shyam Prasad N <sprasad@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Reviewed-by: Paulo Alcantara (SUSE) <pc@xxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # v5.11+ Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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;