From d018028055a21a28adef16b7f95422c426b46d60 Mon Sep 17 00:00:00 2001
From: Stephen Warren <swarren@nvidia.com>
Date: Wed, 11 Jun 2014 12:46:16 -0600
Subject: [PATCH] fs: ext4: fix writing zero-length files

ext4fs_allocate_blocks() always allocates at least one block for a file.
If the file size is zero, this causes total_remaining_blocks to
underflow, which then causes an apparent hang while 2^32 blocks are
allocated.

To solve this, check that total_remaining_blocks is non-zero as part of
the loop condition (i.e. before each loop) rather than at the end of
the loop.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
 fs/ext4/ext4_common.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 1c1172163c..33d69c9c71 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -1380,7 +1380,7 @@ void ext4fs_allocate_blocks(struct ext2_inode *file_inode,
 	unsigned int no_blks_reqd = 0;
 
 	/* allocation of direct blocks */
-	for (i = 0; i < INDIRECT_BLOCKS; i++) {
+	for (i = 0; total_remaining_blocks && i < INDIRECT_BLOCKS; i++) {
 		direct_blockno = ext4fs_get_new_blk_no();
 		if (direct_blockno == -1) {
 			printf("no block left to assign\n");
@@ -1390,8 +1390,6 @@ void ext4fs_allocate_blocks(struct ext2_inode *file_inode,
 		debug("DB %ld: %u\n", direct_blockno, total_remaining_blocks);
 
 		total_remaining_blocks--;
-		if (total_remaining_blocks == 0)
-			break;
 	}
 
 	alloc_single_indirect_block(file_inode, &total_remaining_blocks,
-- 
2.39.5