linux-kernel - Re: [PATCH v2 1/6] ext4: fix WARNING in ext4_expand_extra_isize

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Message-ID: <Y5BF7HXEwZjeKU+a@debian.me>
Date:   Wed, 7 Dec 2022 14:51:08 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Ye Bin <yebin@...weicloud.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        jack@...e.cz, Ye Bin <yebin10@...wei.com>,
        syzbot+4d99a966fd74bdeeec36@...kaller.appspotmail.com
Subject: Re: [PATCH v2 1/6] ext4: fix WARNING in ext4_expand_extra_isize_ea

On Wed, Dec 07, 2022 at 03:40:38PM +0800, Ye Bin wrote:
> From: Ye Bin <yebin10@...wei.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, change EXT4_XATTR_SIZE_MAX from '(1 << 24)' to
> XATTR_SIZE_MAX. As VFS limit extended attribute maxium size to XATTR_SIZE_MAX.
> So we can assume that there will be no extended attribute with a length greater
> than XATTR_SIZE_MAX.

What is the value of (1 << 24)?

The prose reads a rather confused. kmalloc allocates 16M memory, but the
maximum memory size that kmalloc can allocate is 4M, right?

-- 
An old man doll... just what I always wanted! - Clara

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