In the afs dynamic root directory, the ->lookup() function does a DNS check
on the cell being asked for and if the DNS upcall reports an error it will
report an error back to userspace (typically ENOENT).
However, if a failed DNS upcall returns a new-style result, it will return
a valid result, with the status field set appropriately to indicate the
type of failure - and in that case, dns_query() doesn't return an error and
we let stat() complete with no error - which can cause confusion in
userspace as subsequent calls that trigger d_automount then fail with
ENOENT.
Fix this by checking the status result from a valid dns_query() and
returning an error if it indicates a failure.
Fixes: bbb4c4323a4d ("dns: Allow the dns resolver to retrieve a server set")
Reported-by: Markus Suvanto <markus.suvanto@xxxxxxxxx>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=216637
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
---
fs/afs/dynroot.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 34474a061654..4089d77a7a4d 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 >= 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;
}
