Btrfs: make sure we don't overflow the free space cache crc page

The free space cache uses only one page for crcs right now,
which means we can't have a cache file bigger than the
crcs we can fit in the first page.  This adds a check to
enforce that restriction.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 19 insertions, 8 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index dd38d4c3a599..1cb72394498c 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -590,10 +590,25 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
 
         num_pages = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
                 PAGE_CACHE_SHIFT;
+
+        /* Since the first page has all of our checksums and our generation we
+         * need to calculate the offset into the page that we can start writing
+         * our entries.
+         */
+        first_page_offset = (sizeof(u32) * num_pages) + sizeof(u64);
+
         filemap_write_and_wait(inode->i_mapping);
         btrfs_wait_ordered_range(inode, inode->i_size &
                                  ~(root->sectorsize - 1), (u64)-1);
 
+        /* make sure we don't overflow that first page */
+        if (first_page_offset + sizeof(struct btrfs_free_space_entry) >= PAGE_CACHE_SIZE) {
+                /* this is really the same as running out of space, where we also return 0 */
+                printk(KERN_CRIT "Btrfs: free space cache was too big for the crc page\n");
+                ret = 0;
+                goto out_update;
+        }
+
         /* We need a checksum per page. */
         crc = checksums = kzalloc(sizeof(u32) * num_pages, GFP_NOFS);
         if (!crc)
@@ -605,12 +620,6 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                 return -1;
         }
 
-        /* Since the first page has all of our checksums and our generation we
-         * need to calculate the offset into the page that we can start writing
-         * our entries.
-         */
-        first_page_offset = (sizeof(u32) * num_pages) + sizeof(u64);
-
         /* Get the cluster for this block_group if it exists */
         if (block_group && !list_empty(&block_group->cluster_list))
                 cluster = list_entry(block_group->cluster_list.next,
@@ -872,12 +881,14 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
         ret = 1;
 
 out_free:
+        kfree(checksums);
+        kfree(pages);
+
+out_update:
         if (ret != 1) {
                 invalidate_inode_pages2_range(inode->i_mapping, 0, index);
                 BTRFS_I(inode)->generation = 0;
         }
-        kfree(checksums);
-        kfree(pages);
         btrfs_update_inode(trans, root, inode);
         return ret;
 }