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Message-ID: <ac3a58f6-e686-488b-a9ee-fc041024e43d@huawei.com>
Date: Tue, 29 Apr 2025 15:55:18 +0800
From: Zhang Yi <yi.zhang@...wei.com>
To: Liebes Wang <wanghaichi0403@...il.com>, Jan Kara <jack@...e.cz>
CC: <ojaswin@...ux.ibm.com>, Theodore Ts'o <tytso@....edu>, Matthew Wilcox
<willy@...radead.org>, <linux-fsdevel@...r.kernel.org>,
<syzkaller@...glegroups.com>, Ext4 Developers List
<linux-ext4@...r.kernel.org>
Subject: Re: kernel BUG in zero_user_segments
On 2025/4/28 16:14, Jan Kara wrote:
> On Fri 25-04-25 15:29:41, Liebes Wang wrote:
>> Dear Linux maintainers and reviewers:
>> We are reporting a Linux kernel bug titled **kernel BUG in
>> zero_user_segments**, discovered using a modified version of Syzkaller.
>>
>> This bug seems to be duplicated as
>> https://syzkaller.appspot.com/bug?extid=78eeb671facb19832e95, but the test
>> case is much smaller, which may be helpful for analyzing the bug.
>>
>> Linux version: 9d7a0577c9db35c4cc52db90bc415ea248446472
>>
>> The bisection log shows the first introduced commit is
>> 982bf37da09d078570650b691d9084f43805a5de
>> commit 982bf37da09d078570650b691d9084f43805a5de
>> Author: Zhang Yi <yi.zhang@...wei.com>
>> Date: Fri Dec 20 09:16:31 2024 +0800
>>
>> ext4: refactor ext4_punch_hole()
>>
>> The current implementation of ext4_punch_hole() contains complex
>> position calculations and stale error tags. To improve the code's
>> clarity and maintainability, it is essential to clean up the code and
>> improve its readability, this can be achieved by: a) simplifying and
>> renaming variables; b) eliminating unnecessary position calculations;
>> c) writing back all data in data=journal mode, and drop page cache from
>> the original offset to the end, rather than using aligned blocks,
>> d) renaming the stale error tags.
>>
>> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
>> Reviewed-by: Jan Kara <jack@...e.cz>
>> Reviewed-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
>> Link:
>> https://patch.msgid.link/20241220011637.1157197-5-yi.zhang@huaweicloud.com
>> Signed-off-by: Theodore Ts'o <tytso@....edu>
>
> So there's something suspicious about this report. The stacktrace shows
> we've crashed in punch hole code (call from ioctl_preallocate()) but the
> reproducer actually never calls this. Anyway, the reported stack trace ends
> with truncate_inode_partial_folio() -> folio_zero_range() ->
> zero_user_segments(). The assertion that's failing is:
>
> BUG_ON(end1 > page_size(page) || end2 > page_size(page));
After debugging, I found that this problem is caused by punching a hole
with an offset variable larger than max_end on a corrupted ext4 inode,
whose i_size is larger than maxbyte. It will result in a negative length
in the truncate_inode_partial_folio(), which will trigger this problem.
Hi, Liebes!
Thank you for the report. Could you please try the patch below? I have
tested it, and it resolves this issue on my machine.
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 94c7d2d828a6..4ec4a80b6879 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4016,7 +4016,7 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
WARN_ON_ONCE(!inode_is_locked(inode));
/* No need to punch hole beyond i_size */
- if (offset >= inode->i_size)
+ if (offset >= inode->i_size || offset >= max_end)
return 0;
/*
BTW, I also found that the calculation of the max_end variable in
ext4_punch_hole() is wrong for extent inodes. It should be
inode->i_sb->s_maxbytes - sb->s_blocksize instead of
s_bitmap_maxbytes - sb->s_blocksize. I will fix it together.
Thanks,
Yi.
>
> Now it seems that this assertion can indeed easily trigger when we have
> a large folio because truncate_inode_partial_folio() is called to zero out
> tail of the whole folio which can certainly be more than a page. Matthew,
> am I missing something (I guess I am because otherwise I'd expect we'd be
> crashing left and right) or is the folio conversion on this path indeed
> broken?
>
> Honza
>
>>
>> The test case, kernel config and full bisection log are attached.
>>
>> The report is (The full report is attached):
>> EXT4-fs (loop7): mounted filesystem 00000000-0000-0000-0000-000000000000
>> r/w without journal. Quota mode: writeback.
>> EXT4-fs warning (device loop7): ext4_block_to_path:105: block 2147483648 >
>> max in inode 15
>> ------------[ cut here ]------------
>> kernel BUG at ./include/linux/highmem.h:275!
>> Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
>> CPU: 0 UID: 0 PID: 6795 Comm: syz.7.479 Not tainted
>> 6.15.0-rc3-g9d7a0577c9db #1 PREEMPT(voluntary)
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> 1.13.0-1ubuntu1.1 04/01/2014
>> RIP: 0010:zero_user_segments.constprop.0+0x10c/0x290
>> include/linux/highmem.h:275
>> Code: 0f b6 4b 40 ba 00 10 00 00 48 d3 e2 49 89 d7 e8 ba d5 e2 ff 4c 89 fe
>> 4c 89 ef e8 3f d0 e2 ff 4d 39 fd 76 08 e8 a5 d5 e2 ff 90 <0f> 0b e8 9d d5
>> e2 ff be 08 00 00 00 48 89 df e8 a0 9c 1d 00 48 89
>> RSP: 0018:ffff8881235ff678 EFLAGS: 00010216
>> RAX: 000000000000025d RBX: ffffea00056071c0 RCX: ffffc90002e0b000
>> RDX: 0000000000080000 RSI: ffffffff818f7b0b RDI: 0000000000000006
>> RBP: 000000000040b000 R08: 0000000000000000 R09: fffff94000ac0e38
>> R10: 0000000000001000 R11: 0000000000000000 R12: 0000000000000005
>> R13: 000000000040b000 R14: 0000000000000000 R15: 0000000000001000
>> FS: 00007fecef19d700(0000) GS:ffff888543948000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f5e38b40008 CR3: 000000013ebaa001 CR4: 0000000000770ef0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>> PKRU: 80000000
>> Call Trace:
>> <TASK>
>> folio_zero_range include/linux/highmem.h:647 [inline]
>> truncate_inode_partial_folio+0x6da/0xbd0 mm/truncate.c:219
>> truncate_inode_pages_range+0x3fc/0xcc0 mm/truncate.c:387
>> ext4_truncate_page_cache_block_range+0xb3/0x5c0 fs/ext4/inode.c:3974
>> ext4_punch_hole+0x2cd/0xec0 fs/ext4/inode.c:4049
>> ext4_fallocate+0x128d/0x32c0 fs/ext4/extents.c:4766
>> vfs_fallocate+0x3ed/0xd70 fs/open.c:338
>> ioctl_preallocate+0x190/0x200 fs/ioctl.c:290
>> file_ioctl fs/ioctl.c:333 [inline]
>> do_vfs_ioctl+0x149c/0x1850 fs/ioctl.c:885
>> __do_sys_ioctl fs/ioctl.c:904 [inline]
>> __se_sys_ioctl fs/ioctl.c:892 [inline]
>> __x64_sys_ioctl+0x11f/0x200 fs/ioctl.c:892
>> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>> do_syscall_64+0xc1/0x1d0 arch/x86/entry/syscall_64.c:94
>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
>> syz_mount_image$ext4(&(0x7f0000000400)='ext4\x00', &(0x7f00000001c0)='./file0\x00', 0x0, &(0x7f0000000280)={[{@...rnal_ioprio}, {@...optimize_scan}, {@...a_err_ignore}, {@...quota}, {@...rier}]}, 0x1, 0x3cb, &(0x7f00000026c0)="$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")
>> quotactl_fd$Q_SETINFO(0xffffffffffffffff, 0x2, 0x0, &(0x7f0000000080)={0x80000000000002, 0x80000000005, 0x1, 0x6})
>> r0 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file1\x00', 0x42, 0x1ff)
>> ioctl$EXT4_IOC_CHECKPOINT(r0, 0x40305829, &(0x7f0000000080)=0x5)
>> r1 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file1\x00', 0x42, 0x1ff)
>> ioctl$EXT4_IOC_CHECKPOINT(r1, 0x40305829, &(0x7f0000000080)=0x5)
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