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Subject: Re: [PATCH] ext4: fix WARNING in ext4_expand_extra_isize_ea
To:     Jan Kara <jack@suse.cz>, Ye Bin <yebin@huaweicloud.com>
References: <20221201084844.2855621-1-yebin@huaweicloud.com>
 <20221201121928.xk5tte4dj3vmxivs@quack3>
CC:     <tytso@mit.edu>, <adilger.kernel@dilger.ca>,
        <linux-ext4@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <syzbot+4d99a966fd74bdeeec36@syzkaller.appspotmail.com>
From:   "yebin (H)" <yebin10@huawei.com>
Message-ID: <6388AB33.6050302@huawei.com>
Date:   Thu, 1 Dec 2022 21:25:07 +0800
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On 2022/12/1 20:19, Jan Kara wrote:
> Hello!
>
> On Thu 01-12-22 16:48:44, Ye Bin wrote:
>> From: Ye Bin <yebin10@huawei.com>
>>
>> Syzbot found the following issue:
>> ------------[ cut here ]------------
>> WARNING: CPU: 1 PID: 3631 at mm/page_alloc.c:5534 __alloc_pages+0x30a/0x560 mm/page_alloc.c:5534
>> Modules linked in:
>> CPU: 1 PID: 3631 Comm: syz-executor261 Not tainted 6.1.0-rc6-syzkaller-00308-g644e9524388a #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
>> RIP: 0010:__alloc_pages+0x30a/0x560 mm/page_alloc.c:5534
>> RSP: 0018:ffffc90003ccf080 EFLAGS: 00010246
>> RAX: ffffc90003ccf0e0 RBX: 000000000000000c RCX: 0000000000000000
>> RDX: 0000000000000028 RSI: 0000000000000000 RDI: ffffc90003ccf108
>> RBP: ffffc90003ccf198 R08: dffffc0000000000 R09: ffffc90003ccf0e0
>> R10: fffff52000799e21 R11: 1ffff92000799e1c R12: 0000000000040c40
>> R13: 1ffff92000799e18 R14: dffffc0000000000 R15: 1ffff92000799e14
>> FS:  0000555555c10300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007ffc36f70000 CR3: 00000000744ad000 CR4: 00000000003506e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>   <TASK>
>>   __alloc_pages_node include/linux/gfp.h:223 [inline]
>>   alloc_pages_node include/linux/gfp.h:246 [inline]
>>   __kmalloc_large_node+0x8a/0x1a0 mm/slab_common.c:1096
>>   __do_kmalloc_node mm/slab_common.c:943 [inline]
>>   __kmalloc+0xfe/0x1a0 mm/slab_common.c:968
>>   kmalloc include/linux/slab.h:558 [inline]
>>   ext4_xattr_move_to_block fs/ext4/xattr.c:2558 [inline]
>>   ext4_xattr_make_inode_space fs/ext4/xattr.c:2673 [inline]
>>   ext4_expand_extra_isize_ea+0xe3f/0x1cd0 fs/ext4/xattr.c:2765
>>   __ext4_expand_extra_isize+0x2b8/0x3f0 fs/ext4/inode.c:5857
>>   ext4_try_to_expand_extra_isize fs/ext4/inode.c:5900 [inline]
>>   __ext4_mark_inode_dirty+0x51a/0x670 fs/ext4/inode.c:5978
>>   ext4_inline_data_truncate+0x548/0xd00 fs/ext4/inline.c:2021
>>   ext4_truncate+0x341/0xeb0 fs/ext4/inode.c:4221
>>   ext4_process_orphan+0x1aa/0x2d0 fs/ext4/orphan.c:339
>>   ext4_orphan_cleanup+0xb60/0x1340 fs/ext4/orphan.c:474
>>   __ext4_fill_super fs/ext4/super.c:5515 [inline]
>>   ext4_fill_super+0x80ed/0x8610 fs/ext4/super.c:5643
>>   get_tree_bdev+0x400/0x620 fs/super.c:1324
>>   vfs_get_tree+0x88/0x270 fs/super.c:1531
>>   do_new_mount+0x289/0xad0 fs/namespace.c:3040
>>   do_mount fs/namespace.c:3383 [inline]
>>   __do_sys_mount fs/namespace.c:3591 [inline]
>>   __se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3568
>>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>   do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>   </TASK>
>>
>> Reason is allocate 16M memory by kmalloc, but MAX_ORDER is 11, kmalloc
>> can allocate maxium size memory is 4M.
>> XATTR_SIZE_MAX is currently 64k, but EXT4_XATTR_SIZE_MAX is '(1 << 24)',
>> so 'ext4_xattr_check_entries()' regards this length as legal. Then trigger
>> warning in 'ext4_xattr_move_to_block()'.
>> To solve above issue, adjust EXT4_XATTR_SIZE_MAX to '(1 << 22)' which
>> is kmalloc can allocate maxium size.
>>
>> Reported-by: syzbot+4d99a966fd74bdeeec36@syzkaller.appspotmail.com
>> Fixes: 54dd0e0a1b25 ("ext4: add extra checks to ext4_xattr_block_get()")
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
> Thanks for the report and the fix but I think it is actually wrong.  We
> cannot just change EXT4_XATTR_SIZE_MAX because there may be already
> filesystems with this large extended attributes and we'd be suddently
Firstly, thanks for your advice.
I have a question. Since the Linux-2.6.12-rc2 version, XATTR can only be 
set to 64K
at most. I understand that no file's extended attribute exceeds 64K.
> unable to read them. So a better fix would be to use kvmalloc() to allocate
> the memory which is able to accommodate arbitrary allocation size.
>
> Arguably, even better might be to make ext4_xattr_move_to_block() more
> clever because currently it loads attribute into memory from the inode only
> to store it there again. We could just create xattr entry in the block and
> be done with it. But it will be more complex and maybe it's not worth it...
>
> 								Honza
>
>> ---
>>   fs/ext4/xattr.h | 11 ++++++-----
>>   1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
>> index 824faf0b15a8..22f0c89b1184 100644
>> --- a/fs/ext4/xattr.h
>> +++ b/fs/ext4/xattr.h
>> @@ -75,11 +75,12 @@ struct ext4_xattr_entry {
>>    * for file system consistency errors, we use a somewhat bigger value.
>>    * This allows XATTR_SIZE_MAX to grow in the future, but by using this
>>    * instead of INT_MAX for certain consistency checks, we don't need to
>> - * worry about arithmetic overflows.  (Actually XATTR_SIZE_MAX is
>> - * defined in include/uapi/linux/limits.h, so changing it is going
>> - * not going to be trivial....)
>> - */
>> -#define EXT4_XATTR_SIZE_MAX (1 << 24)
>> + * worry about arithmetic overflows. Now, MAX_ORDER is 11 kmalloc can
>> + * allocate maxium size is 4M. (Actually XATTR_SIZE_MAX is defined in
>> + * include/uapi/linux/limits.h, so changing it is going not going to
>> + * be trivial....)
>> +  */
>> +#define EXT4_XATTR_SIZE_MAX (1 << 22)
>>   
>>   /*
>>    * The minimum size of EA value when you start storing it in an external inode
>> -- 
>> 2.31.1
>>