nfsd4: don't try to encode conflicting owner if low on space

I ran into this corner case in testing: in theory clients can provide
state owners up to 1024 bytes long.  In the sessions case there might be
a risk of this pushing us over the DRC slot size.

The conflicting owner isn't really that important, so let's humor a
client that provides a small maxresponsize_cached by allowing ourselves
to return without the conflicting owner instead of outright failing the
operation.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 15 insertions, 4 deletions

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 5d8f9158701d..20aad5a3005f 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1432,7 +1432,8 @@ out:
 #define op_encode_change_info_maxsz     (5)
 #define nfs4_fattr_bitmap_maxsz         (4)
 
-#define op_encode_lockowner_maxsz       (1 + XDR_QUADLEN(IDMAP_NAMESZ))
+/* We'll fall back on returning no lockowner if run out of space: */
+#define op_encode_lockowner_maxsz       (0)
 #define op_encode_lock_denied_maxsz     (8 + op_encode_lockowner_maxsz)
 
 #define nfs4_owner_maxsz                (1 + XDR_QUADLEN(IDMAP_NAMESZ))
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index a90a1e86614a..2f0ea20edb23 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2878,9 +2878,20 @@ nfsd4_encode_lock_denied(struct xdr_stream *xdr, struct nfsd4_lock_denied *ld)
         struct xdr_netobj *conf = &ld->ld_owner;
         __be32 *p;
 
+again:
         p = xdr_reserve_space(xdr, 32 + XDR_LEN(conf->len));
-        if (!p)
+        if (!p) {
+                /*
+                 * Don't fail to return the result just because we can't
+                 * return the conflicting open:
+                 */
+                if (conf->len) {
+                        conf->len = 0;
+                        conf->data = NULL;
+                        goto again;
+                }
                 return nfserr_resource;
+        }
         WRITE64(ld->ld_start);
         WRITE64(ld->ld_length);
         WRITE32(ld->ld_type);
@@ -2888,7 +2899,6 @@ nfsd4_encode_lock_denied(struct xdr_stream *xdr, struct nfsd4_lock_denied *ld)
                 WRITEMEM(&ld->ld_clientid, 8);
                 WRITE32(conf->len);
                 WRITEMEM(conf->data, conf->len);
-                kfree(conf->data);
         }  else {  /* non - nfsv4 lock in conflict, no clientid nor owner */
                 WRITE64((u64)0); /* clientid */
                 WRITE32(0); /* length of owner name */
@@ -2905,7 +2915,7 @@ nfsd4_encode_lock(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_lo
                 nfserr = nfsd4_encode_stateid(xdr, &lock->lk_resp_stateid);
         else if (nfserr == nfserr_denied)
                 nfserr = nfsd4_encode_lock_denied(xdr, &lock->lk_denied);
-
+        kfree(lock->lk_denied.ld_owner.data);
         return nfserr;
 }