lkml.org 
[lkml]   [2022]   [Mar]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
SubjectRe: [PATCH] iomap: fix an infinite loop in iomap_fiemap
From
Hi,

在 2022/3/15 16:04, Gao Xiang 写道:
> Hi Xuenan,
>
> (+ Cc Darrick.. )
>
> On Tue, Mar 15, 2022 at 02:57:45PM +0800, Guo Xuenan wrote:
>> when get fiemap starting from MAX_LFS_FILESIZE, (maxbytes - *len) < start
>> will always true , then *len set zero. because of start offset is byhond
>> file size, for erofs filesystem it will always return iomap.length with
>> zero,iomap iterate will be infinite loop.
> Thanks! If my understanding is correct, we once had a similar
> behavior in compressed inodes and it has been worked around with
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/erofs/zmap.c?h=v5.17-rc8#n762

Yes, your understanding is accurate. But non-compressed inode,still has
the same problem, In my testcase,

set filemap start offset "0x7fffffffffffffff", filemap len will always
be reset to 0;

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/erofs/data.c?h=v5.17-rc8#n267

will always set iomap->length. But i don't think this is the problem of
erofs.

In my opinion, for this situation,  when filemap len is 0, there is no
point to enter a specific filesystem.


Thanks!

> But yeah, if iomap can define or handle post-EOF extent length
> behavior exactly, it would be much better!
>
> So on my side,
>
> Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
>
> (Also you might need to inform iomap maintainer Darrick as well..)
>
> Thanks,
> Gao Xiang
>
>
>> In order to avoid this situation, it is better to calculate the actual
>> mapping length at first. If the len is 0, there is no need to continue
>> the operation.
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 7 PID: 905 at fs/iomap/iter.c:35 iomap_iter+0x97f/0xc70
>> Modules linked in: xfs erofs
>> CPU: 7 PID: 905 Comm: iomap Tainted: G W 5.17.0-rc8 #27
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>> RIP: 0010:iomap_iter+0x97f/0xc70
>> Code: 85 a1 fc ff ff e8 71 be 9c ff 0f 1f 44 00 00 e9 92 fc ff ff e8 62 be 9c ff 0f 0b b8 fb ff ff ff e9 fc f8 ff ff e8 51 be 9c ff <0f> 0b e9 2b fc ff ff e8 45 be 9c ff 0f 0b e9 e1 fb ff ff e8 39 be
>> RSP: 0018:ffff888060a37ab0 EFLAGS: 00010293
>> RAX: 0000000000000000 RBX: ffff888060a37bb0 RCX: 0000000000000000
>> RDX: ffff88807e19a900 RSI: ffffffff81a7da7f RDI: ffff888060a37be0
>> RBP: 7fffffffffffffff R08: 0000000000000000 R09: ffff888060a37c20
>> R10: ffff888060a37c67 R11: ffffed100c146f8c R12: 7fffffffffffffff
>> R13: 0000000000000000 R14: ffff888060a37bd8 R15: ffff888060a37c20
>> FS: 00007fd3cca01540(0000) GS:ffff888108780000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000020010820 CR3: 0000000054b92000 CR4: 00000000000006e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>> <TASK>
>> iomap_fiemap+0x1c9/0x2f0
>> erofs_fiemap+0x64/0x90 [erofs]
>> do_vfs_ioctl+0x40d/0x12e0
>> __x64_sys_ioctl+0xaa/0x1c0
>> do_syscall_64+0x35/0x80
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>> </TASK>
>> ---[ end trace 0000000000000000 ]---
>> watchdog: BUG: soft lockup - CPU#7 stuck for 26s! [iomap:905]
>>
>> Reported-by: Hulk Robot <hulkci@huawei.com>
>> Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
>> ---
>> fs/ioctl.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ioctl.c b/fs/ioctl.c
>> index 1ed097e94af2..7f70e90766ed 100644
>> --- a/fs/ioctl.c
>> +++ b/fs/ioctl.c
>> @@ -171,8 +171,6 @@ int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
>> u32 incompat_flags;
>> int ret = 0;
>>
>> - if (*len == 0)
>> - return -EINVAL;
>> if (start > maxbytes)
>> return -EFBIG;
>>
>> @@ -182,6 +180,9 @@ int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
>> if (*len > maxbytes || (maxbytes - *len) < start)
>> *len = maxbytes - start;
>>
>> + if (*len == 0)
>> + return -EINVAL;
>> +
>> supported_flags |= FIEMAP_FLAG_SYNC;
>> supported_flags &= FIEMAP_FLAGS_COMPAT;
>> incompat_flags = fieinfo->fi_flags & ~supported_flags;
>> --
>> 2.22.0
> .

\
 
 \ /
  Last update: 2022-03-15 10:01    [W:0.075 / U:1.252 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site