Merge tag 'afs-fixes-20231221' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull AFS fixes from David Howells:
 "Improve the interaction of arbitrary lookups in the AFS dynamic root
  that hit DNS lookup failures [1] where kafs behaves differently from
  openafs and causes some applications to fail that aren't expecting
  that. Further, negative DNS results aren't getting removed and are
  causing failures to persist.

   - Always delete unused (particularly negative) dentries as soon as
     possible so that they don't prevent future lookups from retrying.

   - Fix the handling of new-style negative DNS lookups in ->lookup() to
     make them return ENOENT so that userspace doesn't get confused when
     stat succeeds but the following open on the looked up file then
     fails.

   - Fix key handling so that DNS lookup results are reclaimed almost as
     soon as they expire rather than sitting round either forever or for
     an additional 5 mins beyond a set expiry time returning
     EKEYEXPIRED. They persist for 1s as /bin/ls will do a second stat
     call if the first fails"

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216637 [1]
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>

* tag 'afs-fixes-20231221' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry
  afs: Fix dynamic root lookup DNS check
  afs: Fix the dynamic root's d_delete to always delete unused dentries

1 files changed, 17 insertions, 14 deletions

diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 1fa8cf23bd36..1f656005018e 100644
--- a/fs/afs/dynroot.c
+++ b/fs/afs/dynroot.c
@@ -114,6 +114,7 @@ static int afs_probe_cell_name(struct dentry *dentry)
 	struct afs_net *net = afs_d2net(dentry);
 	const char *name = dentry->d_name.name;
 	size_t len = dentry->d_name.len;
+	char *result = NULL;
 	int ret;
 
 	/* Names prefixed with a dot are R/W mounts. */
@@ -131,9 +132,22 @@ static int afs_probe_cell_name(struct dentry *dentry)
 	}
 
 	ret = dns_query(net->net, "afsdb", name, len, "srv=1",
-			NULL, NULL, false);
-	if (ret == -ENODATA || ret == -ENOKEY)
+			&result, NULL, false);
+	if (ret == -ENODATA || ret == -ENOKEY || ret == 0)
 		ret = -ENOENT;
+	if (ret > 0 && ret >= sizeof(struct dns_server_list_v1_header)) {
+		struct dns_server_list_v1_header *v1 = (void *)result;
+
+		if (v1->hdr.zero == 0 &&
+		    v1->hdr.content == DNS_PAYLOAD_IS_SERVER_LIST &&
+		    v1->hdr.version == 1 &&
+		    (v1->status != DNS_LOOKUP_GOOD &&
+		     v1->status != DNS_LOOKUP_GOOD_WITH_BAD))
+			return -ENOENT;
+
+	}
+
+	kfree(result);
 	return ret;
 }
 
@@ -252,20 +266,9 @@ static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
 	return 1;
 }
 
-/*
- * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
- * sleep)
- * - called from dput() when d_count is going to 0.
- * - return 1 to request dentry be unhashed, 0 otherwise
- */
-static int afs_dynroot_d_delete(const struct dentry *dentry)
-{
-	return d_really_is_positive(dentry);
-}
-
 const struct dentry_operations afs_dynroot_dentry_operations = {
 	.d_revalidate	= afs_dynroot_d_revalidate,
-	.d_delete	= afs_dynroot_d_delete,
+	.d_delete	= always_delete_dentry,
 	.d_release	= afs_d_release,
 	.d_automount	= afs_d_automount,
 };