[RFC PATCH V3 2/2] fs : Add sanity checks for block size > PAGE_SIZE

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

We could hit null pointer dereference error during alloc_page_buffers
in : (1) block size > PAGE_SIZE (2) low memory.
Add sanity check for that.

Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
---
 fs/block_dev.c | 1 +
 fs/buffer.c    | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1e86823..2481d42 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1027,6 +1027,7 @@ void bd_set_size(struct block_device *bdev, loff_t size)
 			break;
 		bsize <<= 1;
 	}
+	BUG_ON(bsize > PAGE_SIZE);
 	bdev->bd_block_size = bsize;
 	bdev->bd_inode->i_blkbits = blksize_bits(bsize);
 }
diff --git a/fs/buffer.c b/fs/buffer.c
index 6024877..b039b15 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1571,6 +1571,12 @@ void create_empty_buffers(struct page *page,
 	struct buffer_head *bh, *head, *tail;
 
 	head = alloc_page_buffers(page, blocksize, 1);
+
+	/*
+ 	 * alloc_page_buffers() could return NULL on (1) bs > PAGE_SIZE
+ 	 * (2) low memory case. Ensure that we don't dereference null ptr
+ 	 */  
+	BUG_ON(!head);
 	bh = head;
 	do {
 		bh->b_state |= b_state;
-- 
1.7.11.7