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Message-ID: <66633c9c-f00e-742b-4572-cc0efb153c50@huawei.com>
Date: Fri, 28 Oct 2022 10:17:52 +0800
From: Li Zetao <lizetao1@...wei.com>
To: Liam Howlett <liam.howlett@...cle.com>
CC: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"willy@...radead.org" <willy@...radead.org>,
"catalin.marinas@....com" <catalin.marinas@....com>,
"lizetao1@...wei.com" <lizetao1@...wei.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
"cmllamas@...gle.com" <cmllamas@...gle.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/mmap: Fix memory leak in mmap_region()
Hi,
On 2022/10/27 15:30, Liam Howlett wrote:
> * Li Zetao <lizetao1@...wei.com> [221026 21:55]:
>> There is a memory leak reported by kmemleak:
>>
>> unreferenced object 0xffff88817231ce40 (size 224):
>> comm "mount.cifs", pid 19308, jiffies 4295917571 (age 405.880s)
>> hex dump (first 32 bytes):
>> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> 60 c0 b2 00 81 88 ff ff 98 83 01 42 81 88 ff ff `..........B....
>> backtrace:
>> [<ffffffff81936171>] __alloc_file+0x21/0x250
>> [<ffffffff81937051>] alloc_empty_file+0x41/0xf0
>> [<ffffffff81937159>] alloc_file+0x59/0x710
>> [<ffffffff81937964>] alloc_file_pseudo+0x154/0x210
>> [<ffffffff81741dbf>] __shmem_file_setup+0xff/0x2a0
>> [<ffffffff817502cd>] shmem_zero_setup+0x8d/0x160
>> [<ffffffff817cc1d5>] mmap_region+0x1075/0x19d0
>> [<ffffffff817cd257>] do_mmap+0x727/0x1110
>> [<ffffffff817518b2>] vm_mmap_pgoff+0x112/0x1e0
>> [<ffffffff83adf955>] do_syscall_64+0x35/0x80
>> [<ffffffff83c0006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>>
>> The root cause was traced to an error handing path in mmap_region()
>> when arch_validate_flags() or mas_preallocate() fails. In the shared
>> anonymous mapping sence, vma will be setuped and mapped with a new
>> shared anonymous file via shmem_zero_setup(). So in this case, the
>> file resource needs to be released.
>>
>> Fix it by calling fput(vma->vm_file) when arch_validate_flags() or
>> mas_preallocate() returns an error. And for the beauty of the code,
>> put fput() under mapping_unmap_writable().
> It does look like the unrolling is in the wrong order in that section.
>
>> Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
>> Fixes: c462ac288f2c ("mm: Introduce arch_validate_flags()")
>> Signed-off-by: Li Zetao <lizetao1@...wei.com>
>> ---
>> mm/mmap.c | 10 +++++++---
>> 1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index e270057ed04e..8530195b3ec5 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -2674,6 +2674,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>> error = -EINVAL;
>> if (file)
>> goto close_and_free_vma;I will modify it in the second version
>> + else if (vm_flags & VM_SHARED)
>> + goto put_vma_file;
>> else
>> goto free_vma;
>> }
>> @@ -2682,6 +2684,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>> error = -ENOMEM;
>> if (file)
>> goto close_and_free_vma;
>> + else if (vm_flags & VM_SHARED)
>> + goto put_vma_file;
>> else
>> goto free_vma;
>> }
> I am not happy about this getting more complex as it already duplicates
> too much code.
It's true that my modification would cause the code to further
complicate. I will rework it in the
next version.
>> @@ -2746,13 +2750,13 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>> if (vma->vm_ops && vma->vm_ops->close)
>> vma->vm_ops->close(vma);
>> unmap_and_free_vma:
>> - fput(vma->vm_file);
>> - vma->vm_file = NULL;
>> -
>> /* Undo any partial mapping done by a device driver. */
>> unmap_region(mm, mas.tree, vma, prev, next, vma->vm_start, vma->vm_end);
>> if (vm_flags & VM_SHARED)
> Could we change the above if to "if (file && vm_flags & VM_SHARED)" and
> jump to unmap_and_free_vma "if (vma->vm_file)"? We could then drop your
> new goto label. I still think the reodering is correct and worth while.
>
> Or am I missing something?
Thanks for your constructive comments.
>> mapping_unmap_writable(file->f_mapping);
>> +put_vma_file:
>> + fput(vma->vm_file);
>> + vma->vm_file = NULL;
>> free_vma:
>> vm_area_free(vma);
>> unacct_error:
>> --
>> 2.31.1
Regards,
Li Zetao
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