Re: [RFC PATCH] fs null_blk: Null pointer deference problem in alloc_page_buffers

From: Raghavendra K T
Date: Fri Jan 17 2014 - 13:58:27 EST

On 01/17/2014 11:56 PM, Matias Bjorling wrote:
On 01/17/2014 01:22 AM, Raghavendra K T wrote:

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index a2e69d2..6b0e049 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -535,6 +535,11 @@ static int null_add_dev(void)
if (!nullb)
return -ENOMEM;

+ if (bs > PAGE_SIZE) {
+ WARN(1, "Invalid block size. Setting it to 4096\n");
+ bs = 4096;
+ }

Use PAGESIZE instead, move it to null_init with the other checks and use
pr_warn for issuing the warning.

Thanks. will do that change.


if (queue_mode == NULL_Q_MQ && use_per_node_hctx)
diff --git a/fs/buffer.c b/fs/buffer.c
index 6024877..029c698 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -883,6 +883,7 @@ struct buffer_head *alloc_page_buffers(struct page
*page, unsigned long size,
struct buffer_head *bh, *head;
long offset;

+ BUG_ON(size > PAGE_SIZE);
head = NULL;
offset = PAGE_SIZE;
@@ -1571,6 +1572,7 @@ void create_empty_buffers(struct page *page,
struct buffer_head *bh, *head, *tail;

head = alloc_page_buffers(page, blocksize, 1);
+ BUG_ON(!head);
bh = head;
do {
bh->b_state |= b_state;

It seems? that the physical sector size is always limited to the system
page size.

Why not do the check in add_disk (or __blkdev_get) and fail there,
instead of failing on the first partition check?

I believe you meant checking BUG_ON(block size > PAGE_SIZE) could be done earlier in add_disk/__blkdev_get. I 'll check on that.

For null pointer from alloc_page_buffers part (low in memory condition)
I think we need to retain that.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at