linux-kernel - [PATCH 5.14 185/849] cifs: set a minimum of 120s for next dns resolution

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Date:   Mon, 15 Nov 2021 17:54:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Paulo Alcantara (SUSE)" <pc@....nz>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Steve French <stfrench@...rosoft.com>
Subject: [PATCH 5.14 185/849] cifs: set a minimum of 120s for next dns resolution

From: Paulo Alcantara <pc@....nz>

commit 4ac0536f8874a903a72bddc57eb88db774261e3a upstream.

With commit 506c1da44fee ("cifs: use the expiry output of dns_query to
schedule next resolution") and after triggering the first reconnect,
the next async dns resolution of tcp server's hostname would be
scheduled based on dns_resolver's key expiry default, which happens to
default to 5s on most systems that use key.dns_resolver for upcall.

As per key.dns_resolver.conf(5):

       default_ttl=<number>
              The  number  of  seconds  to  set  as the expiration on a cached
              record.  This will be overridden if the program manages  to  re-
              trieve  TTL  information along with the addresses (if, for exam-
              ple, it accesses the DNS directly).  The default is  5  seconds.
              The value must be in the range 1 to INT_MAX.

Make the next async dns resolution no shorter than 120s as we do not
want to be upcalling too often.

Cc: stable@...r.kernel.org
Fixes: 506c1da44fee ("cifs: use the expiry output of dns_query to schedule next resolution")
Signed-off-by: Paulo Alcantara (SUSE) <pc@....nz>
Reviewed-by: Shyam Prasad N <sprasad@...rosoft.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/cifs/cifsglob.h |    3 ++-
 fs/cifs/connect.c  |    2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -75,7 +75,8 @@
 #define SMB_ECHO_INTERVAL_MAX 600
 #define SMB_ECHO_INTERVAL_DEFAULT 60
 
-/* dns resolution interval in seconds */
+/* dns resolution intervals in seconds */
+#define SMB_DNS_RESOLVE_INTERVAL_MIN     120
 #define SMB_DNS_RESOLVE_INTERVAL_DEFAULT 600
 
 /* maximum number of PDUs in one compound */
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -116,7 +116,7 @@ static int reconn_set_ipaddr_from_hostna
 			 * To make sure we don't use the cached entry, retry 1s
 			 * after expiry.
 			 */
-			ttl = (expiry - now + 1);
+			ttl = max_t(unsigned long, expiry - now, SMB_DNS_RESOLVE_INTERVAL_MIN) + 1;
 	}
 	rc = !rc ? -1 : 0;