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Date:   Tue, 03 Jul 2018 12:24:59 +0900
From:   Seung-Woo Kim <sw0312.kim@samsung.com>
Reply-To: sw0312.kim@samsung.com
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To:     Greg KH <gregkh@linuxfoundation.org>
CC:     linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        torvalds@linux-foundation.org, stable@vger.kernel.org, lwn@lwn.net,
        Jiri Slaby <jslaby@suse.cz>,
        Seung-Woo Kim <sw0312.kim@samsung.com>
Subject: Re: Linux 3.18.111
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Hello,

On 2018년 05월 30일 16:32, Greg KH wrote:
> I'm announcing the release of the 3.18.111 kernel.
> 
> All users of the 3.18 kernel series must upgrade.
> 
> The updated 3.18.y git tree can be found at:
> 	git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git linux-3.18.y
> and can be browsed at the normal kernel.org git web browser:
> 	http://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git;a=summary
> 
> thanks,
> 
> greg k-h
> 
> ------------

<snip.>

>       do d_instantiate/unlock_new_inode combinations safely

Recent my test in 3.18.113 kernel with security smack showed following
crash during mkdir on ext4 fs.

Unable to handle kernel paging request at virtual address ffffffffffffff98
pgd = ffffffc012411000
[ffffffffffffff98] *pgd=0000000000000000, *pud=0000000000000000
------------[ cut here ]------------
Kernel BUG at ffffffc0007d9430 [verbose debug info unavailable]
Internal error: Oops - BUG: 96000005 [#1] PREEMPT SMP
CPU: 0 MPIDR: 80000000 PID: 1237 Comm: mkdir Not tainted
3.18.113-00083-g1bfc02f-dirty #29-Tizen
task: ffffffc02cbc2340 ti: ffffffc02b7fc000 task.ti: ffffffc02b7fc000
PC is at down_read+0x24/0x54
LR is at down_read+0x24/0x54
[...]
Call trace:
[<ffffffc0007d9430>] down_read+0x24/0x54
[<ffffffc00022ff64>] ext4_xattr_get+0x74/0x1f4
[<ffffffc000234838>] ext4_xattr_security_get+0x28/0x38
[<ffffffc0001ab9f0>] generic_getxattr+0x4c/0x60
[<ffffffc0002786a0>] smk_fetch.isra.6+0x8c/0xe0
[<ffffffc000278888>] smack_d_instantiate+0x194/0x324
[<ffffffc000273794>] security_d_instantiate+0x24/0x30
[<ffffffc00019edf4>] d_instantiate_new+0x34/0x94
[<ffffffc0002046b4>] ext4_mkdir+0x284/0x354
[<ffffffc0001959bc>] vfs_mkdir+0xc0/0x150
[<ffffffc00019a108>] SyS_mkdirat+0x88/0xb8
[<ffffffc00019a150>] SyS_mkdir+0x18/0x20
Code: aa0003f3 b00017c0 912e1000 97e38943 (c85f7e60)
---[ end trace b1ad797d63dae9c5 ]---

It is because d_instantiate_new() added from above commit calls
security_d_instantiate() before calling __d_instantiate() and
dentry->d_inode is not yet set and null. In 3.18.113 kernel,
inode->i_op_getxattr() of ext4 is still generic_getxattr() and it only
has dentry parameter without inode, so it tries to access dentry->d_inode.

I did not test with selinux, but selinux also calls
inode->i_op_getxattr() from selinux_d_instantiate(), so maybe there is
also same issue.

Best Regards,
- Seung-Woo Kim

-- 
Seung-Woo Kim
Samsung Research
--