| Message ID | 20231211163412.2766147-3-dhowells@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | afs: Fix dynamic root interaction with failing DNS lookups | expand |
On Mon, Dec 11, 2023 at 12:34 PM David Howells <dhowells@redhat.com> wrote: > > 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@gmail.com> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=216637 > Signed-off-by: David Howells <dhowells@redhat.com> > cc: Marc Dionne <marc.dionne@auristor.com> > cc: linux-afs@lists.infradead.org > --- > 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)) { This needs an additional ret > 0 check, as the comparison may return true with a negative ret if it gets promoted to an unsigned. > + 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; > } Marc
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; }
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@gmail.com> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=216637 Signed-off-by: David Howells <dhowells@redhat.com> cc: Marc Dionne <marc.dionne@auristor.com> cc: linux-afs@lists.infradead.org --- fs/afs/dynroot.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)