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Subject[135/146] brd: limit max_part module param to DISK_MAX_PARTS
2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Namhyung Kim <namhyung@gmail.com>

commit 315980c8688c4b06713c1a5fe9d64cdf8ab57a72 upstream.

The 'max_part' parameter controls the number of maximum partition
a brd device can have. However if a user specifies very large
value it would exceed the limitation of device minor number and
can cause a kernel panic (or, at least, produce invalid device
nodes in some cases).

On my desktop system, following command kills the kernel. On qemu,
it triggers similar oops but the kernel was alive:

$ sudo modprobe brd max_part=100000
BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
IP: [<ffffffff81110a9a>] sysfs_create_dir+0x2d/0xae
PGD 7af1067 PUD 7b19067 PMD 0
Oops: 0000 [#1] SMP
last sysfs file:
CPU 0
Modules linked in: brd(+)
Pid: 44, comm: insmod Tainted: G W 2.6.39-qemu+ #158 Bochs Bochs
RIP: 0010:[<ffffffff81110a9a>] [<ffffffff81110a9a>] sysfs_create_dir+0x2d/0xae
RSP: 0018:ffff880007b15d78 EFLAGS: 00000286
RAX: ffff880007b05478 RBX: ffff880007a52760 RCX: ffff880007b15dc8
RDX: ffff880007a4f900 RSI: ffff880007b15e48 RDI: ffff880007a52760
RBP: ffff880007b15da8 R08: 0000000000000002 R09: 0000000000000000
R10: ffff880007b15e48 R11: ffff880007b05478 R12: 0000000000000000
R13: ffff880007b05478 R14: 0000000000400920 R15: 0000000000000063
FS: 0000000002160880(0063) GS:ffff880007c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000058 CR3: 0000000007b1c000 CR4: 00000000000006b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 0000000000000000 DR7: 0000000000000000
Process insmod (pid: 44, threadinfo ffff880007b14000, task ffff880007acb980)
Stack:
ffff880007b15dc8 ffff880007b05478 ffff880007b15da8 00000000fffffffe
ffff880007a52760 ffff880007b05478 ffff880007b15de8 ffffffff81143c0a
0000000000400920 ffff880007a52760 ffff880007b05478 0000000000000000
Call Trace:
[<ffffffff81143c0a>] kobject_add_internal+0xdf/0x1a0
[<ffffffff81143da1>] kobject_add_varg+0x41/0x50
[<ffffffff81143e6b>] kobject_add+0x64/0x66
[<ffffffff8113bbe7>] blk_register_queue+0x5f/0xb8
[<ffffffff81140f72>] add_disk+0xdf/0x289
[<ffffffffa00040df>] brd_init+0xdf/0x1aa [brd]
[<ffffffffa0004000>] ? 0xffffffffa0003fff
[<ffffffffa0004000>] ? 0xffffffffa0003fff
[<ffffffff8100020a>] do_one_initcall+0x7a/0x12e
[<ffffffff8108516c>] sys_init_module+0x9c/0x1dc
[<ffffffff812ff4bb>] system_call_fastpath+0x16/0x1b
Code: 89 e5 41 55 41 54 53 48 89 fb 48 83 ec 18 48 85 ff 75 04 0f 0b eb fe 48 8b 47 18 49 c7 c4 70 1e 4d 81 48 85 c0 74 04 4c 8b 60 30
8b 44 24 58 45 31 ed 0f b6 c4 85 c0 74 0d 48 8b 43 28 48 89
RIP [<ffffffff81110a9a>] sysfs_create_dir+0x2d/0xae
RSP <ffff880007b15d78>
CR2: 0000000000000058
---[ end trace aebb1175ce1f6739 ]---
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/block/brd.c | 3 +++
1 file changed, 3 insertions(+)
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -585,6 +585,9 @@ static int __init brd_init(void)
if (max_part > 0)
part_shift = fls(max_part);

+ if ((1UL << part_shift) > DISK_MAX_PARTS)
+ return -EINVAL;
+
if (rd_nr > 1UL << (MINORBITS - part_shift))
return -EINVAL;




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