ext2: Fix fs corruption in ext2_get_xip_mem()

Commit 8e3dffc651cb "Ext2: mark inode dirty after the function
dquot_free_block_nodirty is called" unveiled a bug in __ext2_get_block()
called from ext2_get_xip_mem(). That function called ext2_get_block()
mistakenly asking it to map 0 blocks while 1 was intended. Before the
above mentioned commit things worked out fine by luck but after that commit
we started returning that we allocated 0 blocks while we in fact
allocated 1 block and thus allocation was looping until all blocks in
the filesystem were exhausted.

Fix the problem by properly asking for one block and also add assertion
in ext2_get_blocks() to catch similar problems.

Reported-and-tested-by: Andiry Xu <andiry.xu@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

2 files changed, 3 insertions, 0 deletions

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index c260de6d7b6d..8a337640a46a 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -632,6 +632,8 @@ static int ext2_get_blocks(struct inode *inode,
         int count = 0;
         ext2_fsblk_t first_block = 0;
 
+        BUG_ON(maxblocks == 0);
+
         depth = ext2_block_to_path(inode,iblock,offsets,&blocks_to_boundary);
 
         if (depth == 0)
diff --git a/fs/ext2/xip.c b/fs/ext2/xip.c
index 1c3312858fcf..e98171a11cfe 100644
--- a/fs/ext2/xip.c
+++ b/fs/ext2/xip.c
@@ -35,6 +35,7 @@ __ext2_get_block(struct inode *inode, pgoff_t pgoff, int create,
         int rc;
 
         memset(&tmp, 0, sizeof(struct buffer_head));
+        tmp.b_size = 1 << inode->i_blkbits;
         rc = ext2_get_block(inode, pgoff, &tmp, create);
         *result = tmp.b_blocknr;