GFS2: BUG in gfs2_adjust_quota

HighMem pages on i686 do not get mapped to the buffer_heads and this was
causing a NULL pointer dereference when we were trying to memset page buffers
to zero.
We now use zero_user() that kmaps the page and directly manipulates page data.
This patch also fixes a boundary condition that was incorrect.

Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 49667d68769e..b256d6f24288 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -694,10 +694,8 @@ get_a_page:
                 if (!buffer_mapped(bh))
                         goto unlock_out;
                 /* If it's a newly allocated disk block for quota, zero it */
-                if (buffer_new(bh)) {
-                        memset(bh->b_data, 0, bh->b_size);
-                        set_buffer_uptodate(bh);
-                }
+                if (buffer_new(bh))
+                        zero_user(page, pos - blocksize, bh->b_size);
         }
 
         if (PageUptodate(page))
@@ -723,7 +721,7 @@ get_a_page:
 
         /* If quota straddles page boundary, we need to update the rest of the
          * quota at the beginning of the next page */
-        if (offset != 0) { /* first page, offset is closer to PAGE_CACHE_SIZE */
+        if ((offset + sizeof(struct gfs2_quota)) > PAGE_CACHE_SIZE) {
                 ptr = ptr + nbytes;
                 nbytes = sizeof(struct gfs2_quota) - nbytes;
                 offset = 0;