NFSv4: include bitmap in nfsv4 get acl data

The NFSv4 bitmap size is unbounded: a server can return an arbitrary
sized bitmap in an FATTR4_WORD0_ACL request.  Replace using the
nfs4_fattr_bitmap_maxsz as a guess to the maximum bitmask returned by a server
with the inclusion of the bitmap (xdr length plus bitmasks) and the acl data
xdr length to the (cached) acl page data.

This is a general solution to commit e5012d1f "NFSv4.1: update
nfs4_fattr_bitmap_maxsz" and fixes hitting a BUG_ON in xdr_shrink_bufhead
when getting ACLs.

Fix a bug in decode_getacl that returned -EINVAL on ACLs > page when getxattr
was called with a NULL buffer, preventing ACL > PAGE_SIZE from being retrieved.

Cc: stable@kernel.org
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 80 insertions, 47 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index fcc2408d7ab0..3b1080118452 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3426,19 +3426,6 @@ static inline int nfs4_server_supports_acls(struct nfs_server *server)
  */
 #define NFS4ACL_MAXPAGES (XATTR_SIZE_MAX >> PAGE_CACHE_SHIFT)
 
-static void buf_to_pages(const void *buf, size_t buflen,
-                struct page **pages, unsigned int *pgbase)
-{
-        const void *p = buf;
-
-        *pgbase = offset_in_page(buf);
-        p -= *pgbase;
-        while (p < buf + buflen) {
-                *(pages++) = virt_to_page(p);
-                p += PAGE_CACHE_SIZE;
-        }
-}
-
 static int buf_to_pages_noslab(const void *buf, size_t buflen,
                 struct page **pages, unsigned int *pgbase)
 {
@@ -3535,9 +3522,19 @@ out:
         nfs4_set_cached_acl(inode, acl);
 }
 
+/*
+ * The getxattr API returns the required buffer length when called with a
+ * NULL buf. The NFSv4 acl tool then calls getxattr again after allocating
+ * the required buf.  On a NULL buf, we send a page of data to the server
+ * guessing that the ACL request can be serviced by a page. If so, we cache
+ * up to the page of ACL data, and the 2nd call to getxattr is serviced by
+ * the cache. If not so, we throw away the page, and cache the required
+ * length. The next getxattr call will then produce another round trip to
+ * the server, this time with the input buf of the required size.
+ */
 static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t buflen)
 {
-        struct page *pages[NFS4ACL_MAXPAGES];
+        struct page *pages[NFS4ACL_MAXPAGES] = {NULL, };
         struct nfs_getaclargs args = {
                 .fh = NFS_FH(inode),
                 .acl_pages = pages,
@@ -3552,41 +3549,60 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
                 .rpc_argp = &args,
                 .rpc_resp = &res,
         };
-        struct page *localpage = NULL;
-        int ret;
+        int ret = -ENOMEM, npages, i, acl_len = 0;
 
-        if (buflen < PAGE_SIZE) {
-                /* As long as we're doing a round trip to the server anyway,
-                 * let's be prepared for a page of acl data. */
-                localpage = alloc_page(GFP_KERNEL);
-                resp_buf = page_address(localpage);
-                if (localpage == NULL)
-                        return -ENOMEM;
-                args.acl_pages[0] = localpage;
-                args.acl_pgbase = 0;
-                args.acl_len = PAGE_SIZE;
-        } else {
-                resp_buf = buf;
-                buf_to_pages(buf, buflen, args.acl_pages, &args.acl_pgbase);
+        npages = (buflen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+        /* As long as we're doing a round trip to the server anyway,
+         * let's be prepared for a page of acl data. */
+        if (npages == 0)
+                npages = 1;
+
+        for (i = 0; i < npages; i++) {
+                pages[i] = alloc_page(GFP_KERNEL);
+                if (!pages[i])
+                        goto out_free;
+        }
+        if (npages > 1) {
+                /* for decoding across pages */
+                args.acl_scratch = alloc_page(GFP_KERNEL);
+                if (!args.acl_scratch)
+                        goto out_free;
         }
-        ret = nfs4_call_sync(NFS_SERVER(inode)->client, NFS_SERVER(inode), &msg, &args.seq_args, &res.seq_res, 0);
+        args.acl_len = npages * PAGE_SIZE;
+        args.acl_pgbase = 0;
+        /* Let decode_getfacl know not to fail if the ACL data is larger than
+         * the page we send as a guess */
+        if (buf == NULL)
+                res.acl_flags |= NFS4_ACL_LEN_REQUEST;
+        resp_buf = page_address(pages[0]);
+
+        dprintk("%s  buf %p buflen %ld npages %d args.acl_len %ld\n",
+                __func__, buf, buflen, npages, args.acl_len);
+        ret = nfs4_call_sync(NFS_SERVER(inode)->client, NFS_SERVER(inode),
+                             &msg, &args.seq_args, &res.seq_res, 0);
         if (ret)
                 goto out_free;
-        if (res.acl_len > args.acl_len)
-                nfs4_write_cached_acl(inode, NULL, res.acl_len);
+
+        acl_len = res.acl_len - res.acl_data_offset;
+        if (acl_len > args.acl_len)
+                nfs4_write_cached_acl(inode, NULL, acl_len);
         else
-                nfs4_write_cached_acl(inode, resp_buf, res.acl_len);
+                nfs4_write_cached_acl(inode, resp_buf + res.acl_data_offset,
+                                      acl_len);
         if (buf) {
                 ret = -ERANGE;
-                if (res.acl_len > buflen)
+                if (acl_len > buflen)
                         goto out_free;
-                if (localpage)
-                        memcpy(buf, resp_buf, res.acl_len);
+                _copy_from_pages(buf, pages, res.acl_data_offset,
+                                res.acl_len);
         }
-        ret = res.acl_len;
+        ret = acl_len;
 out_free:
-        if (localpage)
-                __free_page(localpage);
+        for (i = 0; i < npages; i++)
+                if (pages[i])
+                        __free_page(pages[i]);
+        if (args.acl_scratch)
+                __free_page(args.acl_scratch);
         return ret;
 }
 
@@ -3617,6 +3633,8 @@ static ssize_t nfs4_proc_get_acl(struct inode *inode, void *buf, size_t buflen)
                 nfs_zap_acl_cache(inode);
         ret = nfs4_read_cached_acl(inode, buf, buflen);
         if (ret != -ENOENT)
+                /* -ENOENT is returned if there is no ACL or if there is an ACL
+                 * but no cached acl data, just the acl length */
                 return ret;
         return nfs4_get_acl_uncached(inode, buf, buflen);
 }
diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index e6161b213ed1..dcaf69309d8e 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -2517,11 +2517,13 @@ static void nfs4_xdr_enc_getacl(struct rpc_rqst *req, struct xdr_stream *xdr,
         encode_compound_hdr(xdr, req, &hdr);
         encode_sequence(xdr, &args->seq_args, &hdr);
         encode_putfh(xdr, args->fh, &hdr);
-        replen = hdr.replen + op_decode_hdr_maxsz + nfs4_fattr_bitmap_maxsz + 1;
+        replen = hdr.replen + op_decode_hdr_maxsz + 1;
         encode_getattr_two(xdr, FATTR4_WORD0_ACL, 0, &hdr);
 
         xdr_inline_pages(&req->rq_rcv_buf, replen << 2,
                 args->acl_pages, args->acl_pgbase, args->acl_len);
+        xdr_set_scratch_buffer(xdr, page_address(args->acl_scratch), PAGE_SIZE);
+
         encode_nops(&hdr);
 }
 
@@ -4957,17 +4959,18 @@ decode_restorefh(struct xdr_stream *xdr)
 }
 
 static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
-                size_t *acl_len)
+                         struct nfs_getaclres *res)
 {
-        __be32 *savep;
+        __be32 *savep, *bm_p;
         uint32_t attrlen,
                  bitmap[3] = {0};
         struct kvec *iov = req->rq_rcv_buf.head;
         int status;
 
-        *acl_len = 0;
+        res->acl_len = 0;
         if ((status = decode_op_hdr(xdr, OP_GETATTR)) != 0)
                 goto out;
+        bm_p = xdr->p;
         if ((status = decode_attr_bitmap(xdr, bitmap)) != 0)
                 goto out;
         if ((status = decode_attr_length(xdr, &attrlen, &savep)) != 0)
@@ -4979,18 +4982,30 @@ static int decode_getacl(struct xdr_stream *xdr, struct rpc_rqst *req,
                 size_t hdrlen;
                 u32 recvd;
 
+                /* The bitmap (xdr len + bitmaps) and the attr xdr len words
+                 * are stored with the acl data to handle the problem of
+                 * variable length bitmaps.*/
+                xdr->p = bm_p;
+                res->acl_data_offset = be32_to_cpup(bm_p) + 2;
+                res->acl_data_offset <<= 2;
+
                 /* We ignore &savep and don't do consistency checks on
                  * the attr length.  Let userspace figure it out.... */
                 hdrlen = (u8 *)xdr->p - (u8 *)iov->iov_base;
+                attrlen += res->acl_data_offset;
                 recvd = req->rq_rcv_buf.len - hdrlen;
                 if (attrlen > recvd) {
-                        dprintk("NFS: server cheating in getattr"
-                                        " acl reply: attrlen %u > recvd %u\n",
+                        if (res->acl_flags & NFS4_ACL_LEN_REQUEST) {
+                                /* getxattr interface called with a NULL buf */
+                                res->acl_len = attrlen;
+                                goto out;
+                        }
+                        dprintk("NFS: acl reply: attrlen %u > recvd %u\n",
                                         attrlen, recvd);
                         return -EINVAL;
                 }
                 xdr_read_pages(xdr, attrlen);
-                *acl_len = attrlen;
+                res->acl_len = attrlen;
         } else
                 status = -EOPNOTSUPP;
 
@@ -6028,7 +6043,7 @@ nfs4_xdr_dec_getacl(struct rpc_rqst *rqstp, struct xdr_stream *xdr,
         status = decode_putfh(xdr);
         if (status)
                 goto out;
-        status = decode_getacl(xdr, rqstp, &res->acl_len);
+        status = decode_getacl(xdr, rqstp, res);
 
 out:
         return status;