Date:   Thu, 11 Jun 2020 12:46:49 +0300
From:   Viacheslav Dubeyko <slava@...eyko.com>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hfs: fix null-ptr-deref in hfs_find_init()

Hi Yang,

On Wed, 2020-06-10 at 20:54 +0800, Yang Yingliang wrote:
> Hi,
> On 2020/6/9 16:06, Viacheslav Dubeyko wrote:
> > Hi Yang,
> > 
> > > On Jun 5, 2020, at 6:01 AM, Yang Yingliang <
> > > yangyingliang@...wei.com> wrote:
> > > 
> > > There is a null-ptr-deref in hfs_find_init():
> > > 
> > > [  107.092729] hfs: continuing without an alternate MDB
> > > [  107.097632] general protection fault, probably for non-
> > > canonical address 0xdffffc0000000008: 0000 [#1] SMP KASAN PTI
> > > [  107.104679] KASAN: null-ptr-deref in range
> > > [0x0000000000000040-0x0000000000000047]
> > > [  107.109100] CPU: 0 PID: 379 Comm: hfs_inject Not tainted
> > > 5.7.0-rc7-00001-g24627f5f2973 #897
> > > [  107.114142] Hardware name: QEMU Standard PC (i440FX + PIIX,
> > > 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org
> > > 04/01/2014
> > > [  107.121095] RIP: 0010:hfs_find_init+0x72/0x170
> > > [  107.123609] Code: c1 ea 03 80 3c 02 00 0f 85 e6 00 00 00 4c 8d
> > > 65 40 48 c7 43 18 00 00 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89
> > > e2 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e a5 00 00 00
> > > 8b 45 40 be c0 0c
> > > [  107.134660] RSP: 0018:ffff88810291f3f8 EFLAGS: 00010202
> > > [  107.137897] RAX: dffffc0000000000 RBX: ffff88810291f468 RCX:
> > > 1ffff110175cdf05
> > > [  107.141874] RDX: 0000000000000008 RSI: ffff88810291f468 RDI:
> > > ffff88810291f480
> > > [  107.145844] RBP: 0000000000000000 R08: 0000000000000000 R09:
> > > ffffed1020381013
> > > [  107.149431] R10: ffff88810291f500 R11: ffffed1020381012 R12:
> > > 0000000000000040
> > > [  107.152315] R13: 0000000000000000 R14: ffff888101c0814a R15:
> > > ffff88810291f468
> > > [  107.155464] FS:  00000000009ea880(0000)
> > > GS:ffff88810c600000(0000) knlGS:0000000000000000
> > > [  107.159795] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [  107.162987] CR2: 00005605a19dd284 CR3: 0000000103a0c006 CR4:
> > > 0000000000020ef0
> > > [  107.166665] Call Trace:
> > > [  107.167969]  ? find_held_lock+0x33/0x1c0
> > > [  107.169972]  hfs_ext_read_extent+0x16b/0xb00
> > > [  107.172092]  ? create_page_buffers+0x14e/0x1b0
> > > [  107.174303]  ? hfs_free_extents+0x280/0x280
> > > [  107.176437]  ? lock_downgrade+0x730/0x730
> > > [  107.178272]  hfs_get_block+0x496/0x8a0
> > > [  107.179972]  block_read_full_page+0x241/0x8d0
> > > [  107.181971]  ? hfs_extend_file+0xae0/0xae0
> > > [  107.183814]  ? end_buffer_async_read_io+0x10/0x10
> > > [  107.185954]  ? add_to_page_cache_lru+0x13f/0x1f0
> > > [  107.188006]  ? add_to_page_cache_locked+0x10/0x10
> > > [  107.190175]  do_read_cache_page+0xc6a/0x1180
> > > [  107.192096]  ? generic_file_read_iter+0x4c0/0x4c0
> > > [  107.194234]  ? hfs_btree_open+0x408/0x1000
> > > [  107.196068]  ? lock_downgrade+0x730/0x730
> > > [  107.197926]  ? wake_bit_function+0x180/0x180
> > > [  107.199845]  ? lockdep_init_map_waits+0x267/0x7c0
> > > [  107.201895]  hfs_btree_open+0x455/0x1000
> > > [  107.203479]  hfs_mdb_get+0x122c/0x1ae8
> > > [  107.205065]  ? hfs_mdb_put+0x350/0x350
> > > [  107.206590]  ? queue_work_node+0x260/0x260
> > > [  107.208309]  ? rcu_read_lock_sched_held+0xa1/0xd0
> > > [  107.210227]  ? lockdep_init_map_waits+0x267/0x7c0
> > > [  107.212144]  ? lockdep_init_map_waits+0x267/0x7c0
> > > [  107.213979]  hfs_fill_super+0x9ba/0x1280
> > > [  107.215444]  ? bdev_name.isra.9+0xf1/0x2b0
> > > [  107.217028]  ? hfs_remount+0x190/0x190
> > > [  107.218428]  ? pointer+0x5da/0x710
> > > [  107.219745]  ? file_dentry_name+0xf0/0xf0
> > > [  107.221262]  ? mount_bdev+0xd1/0x330
> > > [  107.222592]  ? vsnprintf+0x7bd/0x1250
> > > [  107.224007]  ? pointer+0x710/0x710
> > > [  107.225332]  ? down_write+0xe5/0x160
> > > [  107.226698]  ? hfs_remount+0x190/0x190
> > > [  107.228120]  ? snprintf+0x91/0xc0
> > > [  107.229388]  ? vsprintf+0x10/0x10
> > > [  107.230628]  ? sget+0x3af/0x4a0
> > > [  107.231848]  ? hfs_remount+0x190/0x190
> > > [  107.233300]  mount_bdev+0x26e/0x330
> > > [  107.234611]  ? hfs_statfs+0x540/0x540
> > > [  107.236015]  legacy_get_tree+0x101/0x1f0
> > > [  107.237431]  ? security_capable+0x58/0x90
> > > [  107.238832]  vfs_get_tree+0x89/0x2d0
> > > [  107.240082]  ? ns_capable_common+0x5c/0xd0
> > > [  107.241521]  do_mount+0xd8a/0x1720
> > > [  107.242727]  ? lock_downgrade+0x730/0x730
> > > [  107.244116]  ? copy_mount_string+0x20/0x20
> > > [  107.245557]  ? _copy_from_user+0xbe/0x100
> > > [  107.246967]  ? memdup_user+0x47/0x70
> > > [  107.248212]  __x64_sys_mount+0x162/0x1b0
> > > [  107.249537]  do_syscall_64+0xa5/0x4f0
> > > [  107.250742]  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> > > [  107.252369] RIP: 0033:0x44e8ea
> > > [  107.253360] Code: 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 83 c8
> > > ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5
> > > 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff
> > > f7 d8 64 89 01 48
> > > [  107.259240] RSP: 002b:00007ffd910e4c28 EFLAGS: 00000207
> > > ORIG_RAX: 00000000000000a5
> > > [  107.261668] RAX: ffffffffffffffda RBX: 0000000000400400 RCX:
> > > 000000000044e8ea
> > > [  107.263920] RDX: 000000000049321e RSI: 0000000000493222 RDI:
> > > 00007ffd910e4d00
> > > [  107.266177] RBP: 00007ffd910e5d10 R08: 0000000000000000 R09:
> > > 000000000000000a
> > > [  107.268451] R10: 0000000000000001 R11: 0000000000000207 R12:
> > > 0000000000401c40
> > > [  107.270721] R13: 0000000000000000 R14: 00000000006ba018 R15:
> > > 0000000000000000
> > > [  107.273025] Modules linked in:
> > > [  107.274029] Dumping ftrace buffer:
> > > [  107.275121]    (ftrace buffer empty)
> > > [  107.276370] ---[ end trace c5e0b9d684f3570e ]---
> > > 
> > > We need check tree in hfs_find_init().
> > > 
> > > 
https://lore.kernel.org/linux-fsdevel/20180419024358.GA5215@bombadil.infradead.org/
> > > https://marc.info/?l=linux-fsdevel&m=152406881024567&w=2
> > > References: CVE-2018-12928
> > > Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> > > ---
> > > fs/hfs/bfind.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c
> > > index 4af318f..aafa6bd 100644
> > > --- a/fs/hfs/bfind.c
> > > +++ b/fs/hfs/bfind.c
> > > @@ -16,6 +16,8 @@ int hfs_find_init(struct hfs_btree *tree,
> > > struct hfs_find_data *fd)
> > > {
> > > 	void *ptr;
> > > 
> > > +	if (!tree)
> > > +		return -EINVAL;
> > 
> > Looks good. But we have the same issue in HFS+ driver. Could you
> > prepare the patch for HFS+ too?
> 
> OK, I will send a patch for HFS+.
> > 
> > By the way, what is the reason for extents tree pointer to be NULL?
> > Do we have the empty file in this use-case?
> 
> The reproducer is came from 
> https://marc.info/?l=linux-fsdevel&m=152406881024567&w=2 .
> 
> And it's triggered by mounting a crafted hfs file which has a lot of 
> zero data at the end.
> 

I like the fix, but the issue has more complex nature, as far as I can
see. The hfs_ext_read_extent() is trying to access the HFS_SB(inode-
>i_sb)->ext_tree [1]. However, hfs_fill_super() calls the hfs_mdb_get()
that is trying to create Extents Tree. It means that hfs_btree_open()
is trying to access HFS_SB(inode->i_sb)->ext_tree before the real
initialization. Because, namely hfs_btree_open() returns the created
tree object [2]. Did I miss something here? Frankly speaking, I am
slightly confused how it worked before. Maybe, some patch broke the
initial logic?

[1] https://elixir.bootlin.com/linux/latest/source/fs/hfs/extent.c#L200
[2] https://elixir.bootlin.com/linux/latest/source/fs/hfs/mdb.c#L193

Thanks,
Viacheslav Dubeyko.

> 
> Thanks,
> 
> Yang
> 
> > 
> > Thanks,
> > Viacheslav Dubeyko.
> > 
> > > 	fd->tree = tree;
> > > 	fd->bnode = NULL;
> > > 	ptr = kmalloc(tree->max_key_len * 2 + 4, GFP_KERNEL);
> > > -- 
> > > 1.8.3
> > > 
> > 
> > .
> 
> 

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