afs: prevent double cell registration

kafs doesn't check if the cell already exists - so if you do an echo "add
newcell.org 1.2.3.4" >/proc/fs/afs/cells it will try to create this cell
again.  kobject will also complain about a double registration.  To prevent
such problems, return -EEXIST in that case.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index 970d38f30565..788865df1bc9 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -127,14 +127,20 @@ struct afs_cell *afs_cell_create(const char *name, char *vllist)
 
         _enter("%s,%s", name, vllist);
 
+        down_write(&afs_cells_sem);
+        read_lock(&afs_cells_lock);
+        list_for_each_entry(cell, &afs_cells, link) {
+                if (strcasecmp(cell->name, name) == 0)
+                        goto duplicate_name;
+        }
+        read_unlock(&afs_cells_lock);
+
         cell = afs_cell_alloc(name, vllist);
         if (IS_ERR(cell)) {
                 _leave(" = %ld", PTR_ERR(cell));
                 return cell;
         }
 
-        down_write(&afs_cells_sem);
-
         /* add a proc directory for this cell */
         ret = afs_proc_cell_setup(cell);
         if (ret < 0)
@@ -167,6 +173,11 @@ error:
         kfree(cell);
         _leave(" = %d", ret);
         return ERR_PTR(ret);
+
+duplicate_name:
+        read_unlock(&afs_cells_lock);
+        up_write(&afs_cells_sem);
+        return ERR_PTR(-EEXIST);
 }
 
 /*