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

Greg Kroah-Hartman
2021-11-16T01:43:14Z

From: Paulo Alcantara <pc@cjr.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@vger.kernel.org
Fixes: 506c1da44fee ("cifs: use the expiry output of dns_query to schedule next resolution")
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;