Re: [RFC PATCH V2] fs null_blk: Null pointer deference problem inalloc_page_buffers

[Matias Bjorling]

On 01/20/2014 04:58 AM, Raghavendra K T wrote:
>  If we load the null_blk module with bs=8k we get following oops:
> [ 3819.812190] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> [ 3819.812387] IP: [<ffffffff81170aa5>] create_empty_buffers+0x28/0xaf
> [ 3819.812527] PGD 219244067 PUD 215a06067 PMD 0
> [ 3819.812640] Oops: 0000 [#1] SMP
> [ 3819.812772] Modules linked in: null_blk(+)
> 
>  Fix that by resetting block size to PAGE_SIZE if it is greater than PAGE_SIZE
>  Also add sanity checks for block size > PAGE_SIZE.

We should probably split the patch into two. Giving a better description
to each of the changes.

> 
> Reported-by: Sumanth <sumantk2@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> ---
>  Changes in V2:
>   - Change hardcode 4k to PAGE_SIZE (Jeff, Matias)
>   - use pr_warn and move bs setting to null_init (Matias)
>   - Move bs > PAGE_SIZE to bd_set_size based on Matias' suggestion.
>  
>  The full oops below:
>  [ 3819.812190] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> [ 3819.812387] IP: [<ffffffff81170aa5>] create_empty_buffers+0x28/0xaf
> [ 3819.812527] PGD 219244067 PUD 215a06067 PMD 0 
> [ 3819.812640] Oops: 0000 [#1] SMP 
> [ 3819.812772] Modules linked in: null_blk(+)
> [ 3819.812872] CPU: 8 PID: 1179 Comm: modprobe Not tainted 3.13.0-rc6+ #144
> [ 3819.813008] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007
> [ 3819.813071] task: ffff8800376add40 ti: ffff8800374c8000 task.ti: ffff8800374c8000
> [ 3819.813071] RIP: 0010:[<ffffffff81170aa5>]  [<ffffffff81170aa5>] create_empty_buffers+0x28/0xaf
> [ 3819.813071] RSP: 0018:ffff8800374c9758  EFLAGS: 00010292
> [ 3819.813071] RAX: 0000000000000000 RBX: ffffea000368e200 RCX: 000000000000000d
> [ 3819.813071] RDX: 0000000000000000 RSI: 0000000000002000 RDI: ffffea000368e200
> [ 3819.813071] RBP: ffff8800374c9778 R08: 0000000000000000 R09: 0000000000003012
> [ 3819.813071] R10: 0000000000003012 R11: ffff8800dbad0240 R12: 0000000000000000
> [ 3819.813071] R13: 0000000000000000 R14: 00000000000201d0 R15: 0000000000000000
> [ 3819.813071] FS:  00007fa0f79dd700(0000) GS:ffff88011bd00000(0000) knlGS:0000000000000000
> [ 3819.813071] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 3819.813071] CR2: 0000000000000008 CR3: 0000000215b0e000 CR4: 00000000000407e0
> [ 3819.813071] Stack:
> [ 3819.813071]  0000000000003012 ffffea000368e200 ffffea000368e200 0000000000000000
> [ 3819.813071]  ffff8800374c9798 ffffffff81171047 0000000000016378 ffff8800dbad0240
> [ 3819.813071]  ffff8800374c9848 ffffffff81172deb 00000000000201d0 ffff8800376add40
> [ 3819.813071] Call Trace:
> [ 3819.813071]  [<ffffffff81171047>] create_page_buffers+0x36/0x48
> [ 3819.813071]  [<ffffffff81172deb>] block_read_full_page+0x38/0x1ed
> [ 3819.813071]  [<ffffffff8117520a>] ? I_BDEV+0xd/0xd
> [ 3819.813071]  [<ffffffff8111580d>] ? __inc_zone_page_state+0x1e/0x20
> [ 3819.813071]  [<ffffffff81108e31>] ? get_page+0x24/0x29
> [ 3819.813071]  [<ffffffff81108e5a>] ? __lru_cache_add+0x24/0x44
> [ 3819.813071]  [<ffffffff811759f7>] blkdev_readpage+0x18/0x1a
> [ 3819.813071]  [<ffffffff810fe753>] do_read_cache_page+0x88/0x12c
> [ 3819.813071]  [<ffffffff81115a33>] ? zone_statistics+0x7c/0x83
> [ 3819.813071]  [<ffffffff811759df>] ? blkdev_write_begin+0x25/0x25
> [ 3819.813071]  [<ffffffff810fe838>] read_cache_page_async+0x19/0x1b
> [ 3819.813071]  [<ffffffff810fe848>] read_cache_page+0xe/0x18
> [ 3819.813071]  [<ffffffff812b0ca5>] read_dev_sector+0x2d/0x85
> [ 3819.813071]  [<ffffffff812b34cf>] read_lba+0x81/0xdd
> [ 3819.813071]  [<ffffffff812b38f7>] ? find_valid_gpt+0x9a/0x51d
> [ 3819.813071]  [<ffffffff812b3915>] find_valid_gpt+0xb8/0x51d
> [ 3819.813071]  [<ffffffff812b3de6>] efi_partition+0x6c/0x38e
> [ 3819.813071]  [<ffffffff812c9609>] ? vsnprintf+0x81/0x3d6
> [ 3819.813071]  [<ffffffff812c9fe5>] ? snprintf+0x34/0x36
> [ 3819.813071]  [<ffffffff812b1a3a>] check_partition+0x113/0x1cd
> [ 3819.813071]  [<ffffffff812b1699>] rescan_partitions+0xc1/0x2a7
> [ 3819.813071]  [<ffffffff81176607>] __blkdev_get+0x1bd/0x3e3
> [ 3819.813071]  [<ffffffff81176a0c>] blkdev_get+0x1df/0x2d8
> [ 3819.813071]  [<ffffffff8115d1ea>] ? unlock_new_inode+0x5c/0x61
> [ 3819.813071]  [<ffffffff813a2a2f>] ? put_device+0x17/0x19
> [ 3819.813071]  [<ffffffff812ae811>] ? disk_put_part+0x12/0x14
> [ 3819.813071]  [<ffffffff812af717>] add_disk+0x2af/0x3f0
> [ 3819.813071]  [<ffffffffa00033a4>] null_init+0x3a4/0x3e5 [null_blk]
> [ 3819.813071]  [<ffffffffa0003000>] ? 0xffffffffa0002fff
> [ 3819.813071]  [<ffffffff810002e3>] do_one_initcall+0xb3/0x154
> [ 3819.813071]  [<ffffffff810732c9>] ? __blocking_notifier_call_chain+0x56/0x60
> [ 3819.813071]  [<ffffffff810ade71>] load_module+0x1c4f/0x1f92
> [ 3819.813071]  [<ffffffff810abc11>] ? show_initstate+0x47/0x47
> [ 3819.813071]  [<ffffffff810ae27b>] SyS_init_module+0xc7/0xc9
> [ 3819.813071]  [<ffffffff816c8a69>] system_call_fastpath+0x16/0x1b
> [ 3819.813071] Code: 5f 5d c3 66 66 66 66 90 55 48 89 e5 41 55 41 54 49 89 d4 ba 01 00 00 00 53 48 89 fb 41 52 e8 3b ff ff ff 49 89 c5 eb 03 48 89 d0 <48> 8b 50 08 4c 09 20 48 85 d2 75 f1 4c 89 68 08 48 8b 7b 08 4d 
> [ 3819.813071] RIP  [<ffffffff81170aa5>] create_empty_buffers+0x28/0xaf
> [ 3819.813071]  RSP <ffff8800374c9758>
> [ 3819.813071] CR2: 0000000000000008
> [ 3819.837847] ---[ end trace e3c8b9f8f8af88d6 ]---
> 
>  Your suggestion/Comments welcome.
> 
>  drivers/block/null_blk.c | 4 ++++
>  fs/block_dev.c           | 1 +
>  fs/buffer.c              | 1 +
>  3 files changed, 6 insertions(+)
> 
> diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
> index a2e69d2..bcae726 100644
> --- a/drivers/block/null_blk.c
> +++ b/drivers/block/null_blk.c
> @@ -622,6 +622,10 @@ static int __init null_init(void)
>  		irqmode = NULL_IRQ_NONE;
>  	}
>  #endif
> +	if (bs > PAGE_SIZE) {
> +		pr_warn("Invalid block size. Setting it to %lu\n", PAGE_SIZE);
> +		bs = PAGE_SIZE;
> +	}

Could the warning say something like:

pr_warn("null_blk: invalid block size\n");
pr_warn("null_blk: defaults block size to &lu\n");

then it follows the same patterns as the other errors.

>  
>  	if (queue_mode == NULL_Q_MQ && use_per_node_hctx) {
>  		if (submit_queues < nr_online_nodes) {
> 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..8b7ada1 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1571,6 +1571,7 @@ 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;
> 

For the check patch, the description could mention some text on why we
hit this error case and why we check for it.

Thank you.

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