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afs: Fix dynamic root lookup DNS check

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[ Upstream commit 74cef6872ceaefb5b6c5c60641371ea28702d358 ]

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: bbb4c4323a ("dns: Allow the dns resolver to retrieve a server set")
Reported-by: Markus Suvanto <markus.suvanto@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=216637
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Markus Suvanto <markus.suvanto@gmail.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
David Howells 2023-12-11 15:15:02 +00:00 committed by Greg Kroah-Hartman
parent 82d64cbe48
commit eec7ef60d2
1 changed files with 16 additions and 2 deletions
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18
fs/afs/dynroot.c
View File

@ -20,6 +20,7 @@ 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. */
@ -37,9 +38,22 @@ 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;
}