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Subject[RFC PATCH V3 0/2] Fix null pointer deference problem
Date

When we load null_blk with bs > PAGE_SIZE we get oops like below.
This patch series fixes that. Also we add some sanity check for the cases
where bs > PAGE_SIZE causes problem.

full 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(+)
[ 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 ]---

I would like to thank Matias and Jeff for their vaulable comments.

Changes in V3:
- split patch, Change warning format (Matias)
- Add more description for null pointer check (Matias)
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.

Your suggestion/Comments welcome.

Raghavendra K T (2):
null_blk: Null pointer deference problem in alloc_page_buffers
fs : Add sanity checks for block size > PAGE_SIZE

drivers/block/null_blk.c | 5 +++++
fs/block_dev.c | 1 +
fs/buffer.c | 6 ++++++
3 files changed, 12 insertions(+)

--
1.7.11.7



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