nfsd race fixes: ext2

* make ext2_new_inode() put the inode into icache in locked state
* do not unlock until the inode is fully set up; otherwise nfsd
might pick it in half-baked state.
* make sure that ext2_new_inode() does *not* lead to two inodes with the
same inumber hashed at the same time; otherwise a bogus fhandle coming
from nfsd might race with inode creation:

nfsd: iget_locked() creates inode
nfsd: try to read from disk, block on that.
ext2_new_inode(): allocate inode with that inumber
ext2_new_inode(): insert it into icache, set it up and dirty
ext2_write_inode(): get the relevant part of inode table in cache,
set the entry for our inode (and start writing to disk)
nfsd: get CPU again, look into inode table, see nice and sane on-disk
inode, set the in-core inode from it

oops - we have two in-core inodes with the same inumber live in icache,
both used for IO.  Welcome to fs corruption...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c
index 8d0add62587..c454d5db28a 100644
--- a/fs/ext2/ialloc.c
+++ b/fs/ext2/ialloc.c
@@ -585,7 +585,10 @@ got:
 	spin_lock(&sbi->s_next_gen_lock);
 	inode->i_generation = sbi->s_next_generation++;
 	spin_unlock(&sbi->s_next_gen_lock);
-	insert_inode_hash(inode);
+	if (insert_inode_locked(inode) < 0) {
+		err = -EINVAL;
+		goto fail_drop;
+	}
 
 	if (DQUOT_ALLOC_INODE(inode)) {
 		err = -EDQUOT;
@@ -612,6 +615,7 @@ fail_drop:
 	DQUOT_DROP(inode);
 	inode->i_flags |= S_NOQUOTA;
 	inode->i_nlink = 0;
+	unlock_new_inode(inode);
 	iput(inode);
 	return ERR_PTR(err);