Re: [PATCH v2] tmpfs: allow decoding a file handle of an unlinked file

[Amir Goldstein <amir73il@gmail.com>]

On Fri, Jan 5, 2018 at 5:40 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> On Mon, Nov 13, 2017 at 8:43 AM, Amir Goldstein <amir73il@gmail.com> wrote:
>> tmpfs uses the helper d_find_alias() to find a dentry from a decoded
>> inode, but d_find_alias() skips unhashed dentries, so unlinked files
>> cannot be decoded from a file handle.
>>
>> This can be reproduced using xfstests test program open_by_handle:
>> $ open_by handle -c /tmp/testdir
>> $ open_by_handle -dk /tmp/testdir
>> open_by_handle(/tmp/testdir/file000000) returned 116 incorrectly on an
>> unlinked open file!
>>
>> To fix this, if d_find_alias() can't find a hashed alias, call
>> d_find_any_alias() to return an unhashed one.
>>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Al Viro <viro@zeniv.linux.org.uk>
>> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
>> ---
>>
>> Al, Miklos,
>>
>> Can either of you take this patch through your tree?
>>
>> Thanks,
>> Amir.
>>
>> Changes since v1:
>> - Prefer a hashed alias (James)
>> - Use existing d_find_any_alias() helper
>>
>>  mm/shmem.c | 11 ++++++++++-
>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 07a1d22807be..5d3fa4099f54 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -3404,6 +3404,15 @@ static int shmem_match(struct inode *ino, void *vfh)
>>         return ino->i_ino == inum && fh[0] == ino->i_generation;
>>  }
>>
>> +/* Find any alias of inode, but prefer a hashed alias */
>> +static struct dentry *shmem_find_alias(struct inode *inode)
>> +{
>> +       struct dentry *alias = d_find_alias(inode);
>> +
>> +       return alias ?: d_find_any_alias(inode);
>> +}
>> +
>> +
>>  static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
>>                 struct fid *fid, int fh_len, int fh_type)
>>  {
>> @@ -3420,7 +3429,7 @@ static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
>>         inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
>>                         shmem_match, fid->raw);
>>         if (inode) {
>> -               dentry = d_find_alias(inode);
>> +               dentry = shmem_find_alias(inode);
>>                 iput(inode);
>>         }
>>
>> --
>
> Hugh,
>
> Did you get a chance to look at this patch?
>
> The test for decoding a file handle of an unlinked file has already been
> merged to xfstest generic/467 and the test is failing on tmpfs without this
> change.
>
> Can you please take or ACK this patch?
>

Ping.

Real problem.

Trivial fix.

Al, Can you take this patch?

Thanks,
Amir.

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