RDS: Copy rds_iovecs into kernel memory instead of rereading from userspace

Change rds_rdma_pages to take a passed-in rds_iovec array instead
of doing copy_from_user itself.

Change rds_cmsg_rdma_args to copy rds_iovec array once only. This
eliminates the possibility of userspace changing it after our
sanity checks.

Implement stack-based storage for small numbers of iovecs, based
on net/socket.c, to save an alloc in the extremely common case.

Although this patch reduces iovec copies in cmsg_rdma_args to 1,
we still do another one in rds_rdma_extra_size. Getting rid of
that one will be trickier, so it'll be a separate patch.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 65 insertions, 39 deletions

diff --git a/net/rds/rdma.c b/net/rds/rdma.c
index 334acdd32ab6..caa4d9866d92 100644
--- a/net/rds/rdma.c
+++ b/net/rds/rdma.c
@@ -479,13 +479,38 @@ void rds_atomic_free_op(struct rm_atomic_op *ao)
 
 
 /*
- * Count the number of pages needed to describe an incoming iovec.
+ * Count the number of pages needed to describe an incoming iovec array.
  */
-static int rds_rdma_pages(struct rds_rdma_args *args)
+static int rds_rdma_pages(struct rds_iovec iov[], int nr_iovecs)
+{
+        int tot_pages = 0;
+        unsigned int nr_pages;
+        unsigned int i;
+
+        /* figure out the number of pages in the vector */
+        for (i = 0; i < nr_iovecs; i++) {
+                nr_pages = rds_pages_in_vec(&iov[i]);
+                if (nr_pages == 0)
+                        return -EINVAL;
+
+                tot_pages += nr_pages;
+
+                /*
+                 * nr_pages for one entry is limited to (UINT_MAX>>PAGE_SHIFT)+1,
+                 * so tot_pages cannot overflow without first going negative.
+                 */
+                if (tot_pages < 0)
+                        return -EINVAL;
+        }
+
+        return tot_pages;
+}
+
+int rds_rdma_extra_size(struct rds_rdma_args *args)
 {
         struct rds_iovec vec;
         struct rds_iovec __user *local_vec;
-        unsigned int tot_pages = 0;
+        int tot_pages = 0;
         unsigned int nr_pages;
         unsigned int i;
 
@@ -507,16 +532,11 @@ static int rds_rdma_pages(struct rds_rdma_args *args)
                  * nr_pages for one entry is limited to (UINT_MAX>>PAGE_SHIFT)+1,
                  * so tot_pages cannot overflow without first going negative.
                  */
-                if ((int)tot_pages < 0)
+                if (tot_pages < 0)
                         return -EINVAL;
         }
 
-        return tot_pages;
-}
-
-int rds_rdma_extra_size(struct rds_rdma_args *args)
-{
-        return rds_rdma_pages(args) * sizeof(struct scatterlist);
+        return tot_pages * sizeof(struct scatterlist);
 }
 
 /*
@@ -527,13 +547,12 @@ int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
                           struct cmsghdr *cmsg)
 {
         struct rds_rdma_args *args;
-        struct rds_iovec vec;
         struct rm_rdma_op *op = &rm->rdma;
         int nr_pages;
         unsigned int nr_bytes;
         struct page **pages = NULL;
-        struct rds_iovec __user *local_vec;
-        unsigned int nr;
+        struct rds_iovec iovstack[UIO_FASTIOV], *iovs = iovstack;
+        int iov_size;
         unsigned int i, j;
         int ret = 0;
 
@@ -553,7 +572,22 @@ int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
                 goto out;
         }
 
-        nr_pages = rds_rdma_pages(args);
+        /* Check whether to allocate the iovec area */
+        iov_size = args->nr_local * sizeof(struct rds_iovec);
+        if (args->nr_local > UIO_FASTIOV) {
+                iovs = sock_kmalloc(rds_rs_to_sk(rs), iov_size, GFP_KERNEL);
+                if (!iovs) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
+        }
+
+        if (copy_from_user(iovs, (struct rds_iovec __user *)(unsigned long) args->local_vec_addr, iov_size)) {
+                ret = -EFAULT;
+                goto out;
+        }
+
+        nr_pages = rds_rdma_pages(iovs, args->nr_local);
         if (nr_pages < 0) {
                 ret = -EINVAL;
                 goto out;
@@ -606,50 +640,40 @@ int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
                (unsigned long long)args->remote_vec.addr,
                op->op_rkey);
 
-        local_vec = (struct rds_iovec __user *)(unsigned long) args->local_vec_addr;
-
         for (i = 0; i < args->nr_local; i++) {
-                if (copy_from_user(&vec, &local_vec[i],
-                                   sizeof(struct rds_iovec))) {
-                        ret = -EFAULT;
-                        goto out;
-                }
-
-                nr = rds_pages_in_vec(&vec);
-                if (nr == 0) {
-                        ret = -EINVAL;
-                        goto out;
-                }
+                struct rds_iovec *iov = &iovs[i];
+                /* don't need to check, rds_rdma_pages() verified nr will be +nonzero */
+                unsigned int nr = rds_pages_in_vec(iov);
 
-                rs->rs_user_addr = vec.addr;
-                rs->rs_user_bytes = vec.bytes;
+                rs->rs_user_addr = iov->addr;
+                rs->rs_user_bytes = iov->bytes;
 
                 /* If it's a WRITE operation, we want to pin the pages for reading.
                  * If it's a READ operation, we need to pin the pages for writing.
                  */
-                ret = rds_pin_pages(vec.addr, nr, pages, !op->op_write);
+                ret = rds_pin_pages(iov->addr, nr, pages, !op->op_write);
                 if (ret < 0)
                         goto out;
 
-                rdsdebug("RDS: nr_bytes %u nr %u vec.bytes %llu vec.addr %llx\n",
-                       nr_bytes, nr, vec.bytes, vec.addr);
+                rdsdebug("RDS: nr_bytes %u nr %u iov->bytes %llu iov->addr %llx\n",
+                         nr_bytes, nr, iov->bytes, iov->addr);
 
-                nr_bytes += vec.bytes;
+                nr_bytes += iov->bytes;
 
                 for (j = 0; j < nr; j++) {
-                        unsigned int offset = vec.addr & ~PAGE_MASK;
+                        unsigned int offset = iov->addr & ~PAGE_MASK;
                         struct scatterlist *sg;
 
                         sg = &op->op_sg[op->op_nents + j];
                         sg_set_page(sg, pages[j],
-                                        min_t(unsigned int, vec.bytes, PAGE_SIZE - offset),
+                                        min_t(unsigned int, iov->bytes, PAGE_SIZE - offset),
                                         offset);
 
-                        rdsdebug("RDS: sg->offset %x sg->len %x vec.addr %llx vec.bytes %llu\n",
-                               sg->offset, sg->length, vec.addr, vec.bytes);
+                        rdsdebug("RDS: sg->offset %x sg->len %x iov->addr %llx iov->bytes %llu\n",
+                               sg->offset, sg->length, iov->addr, iov->bytes);
 
-                        vec.addr += sg->length;
-                        vec.bytes -= sg->length;
+                        iov->addr += sg->length;
+                        iov->bytes -= sg->length;
                 }
 
                 op->op_nents += nr;
@@ -665,6 +689,8 @@ int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
         op->op_bytes = nr_bytes;
 
 out:
+        if (iovs != iovstack)
+                sock_kfree_s(rds_rs_to_sk(rs), iovs, iov_size);
         kfree(pages);
         if (ret)
                 rds_rdma_free_op(op);