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 4k if it is greater than PAGE_SIZE
Also adding BUG_ON for null point dereference places.
Reported-by: Sumanth <sumantk2@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
---
Please note that alloc_page_buffers can return NULL on
(1) when we are out of memory
(2) block size > PAGE_SIZE
In any case create_empty_buffers function will end up in dereferencing
null pointer.
May be there could be some saner approach to solve this, I am adding
BUG_ON ( Not sure if that is good idea considering we hate that)
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 | 5 +++++
fs/buffer.c | 2 ++
2 files changed, 7 insertions(+)
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;
+ }
+
spin_lock_init(&nullb->lock);
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);
try_again:
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;
--
1.7.11.7
--
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