Re: [PATCH v2] ecryptfs: sync before truncating lower inode

[Tyler Hicks]

On 11/15/2017 06:58 PM, Dmitry Torokhov wrote:
> On Wed, Apr 26, 2017 at 11:02 AM, Andrey Pronin <apronin@xxxxxxxxxxxx> wrote:
>> If the updated ecryptfs header data is not written to disk before
>> the lower file is truncated, a crash may leave the filesystem
>> in the state when the lower file truncation is journaled, while
>> the changes to the ecryptfs header are lost (if the underlying
>> filesystem is ext4 in data=ordered mode, for example). As a result,
>> upon remounting and repairing the file may have a pre-truncation
>> length and garbage data after the post-truncation end.
>>
>> To reproduce, make a snapshot of the underlying ext4 filesystem
>> mounted with data=ordered while asynchronously truncating to zero a
>> group of files in ecryptfs mounted on top. Mount ecryptfs for the
>> snapshot and check the contents of the group of files that was
>> being truncated. The following script reproduces it in almost 100%
>> of runs:
>>
>> cd /tmp
>> mkdir -p ./loop
>> dd if=/dev/zero of=./file.img bs=1M count=10
>> PW=secret
>>
>> LOOPDEV=`losetup --find --show ./file.img`
>> mkfs -t ext4 $LOOPDEV
>> mount -t ext4 -o rw,nodev,relatime,seclabel,commit=600,data=ordered\
>>  $LOOPDEV ./loop
>> mkdir -p ./loop/vault ./loop/mount
>> mount -t ecryptfs -o rw,relatime,seclabel,ecryptfs_cipher=aes,\
>> ecryptfs_key_bytes=16,ecryptfs_unlink_sigs,ecryptfs_passthrough=no,\
>> ecryptfs_enable_filename_crypto=no,passphrase_passwd="$PW",no_sig_cache\
>>  ./loop/vault ./loop/mount
>> for i in `seq 1 100`; do echo $i > ./loop/mount/test.$i; done
>> sync
>> for i in `seq 100 -1 1`; do truncate -s 0 ./loop/mount/test.$i; done &
>> sleep 0.1; sync; cp ./file.img ./file.snap; sleep 1
>> umount ./loop/mount
>> umount ./loop
>> losetup -d $LOOPDEV
>>
>> LOOPDEV=`losetup --find --show ./file.snap`
>> mount -t ext4 -o rw,nodev,relatime,seclabel,commit=600,data=ordered\
>>  $LOOPDEV ./loop
>> mount -t ecryptfs -o rw,relatime,seclabel,ecryptfs_cipher=aes,\
>> ecryptfs_key_bytes=16,ecryptfs_unlink_sigs,ecryptfs_passthrough=no,\
>> ecryptfs_enable_filename_crypto=no,passphrase_passwd="$PW",no_sig_cache\
>>  ./loop/vault ./loop/mount
>> for i in `seq 1 100`; do
>>   if [ `stat -c %s ./loop/mount/test.$i` != 0 ] &&
>>      [ `cat ./loop/mount/test.$i` != $i ]; then
>>        echo -n "!!! garbage at $i: ";  cat ./loop/mount/test.$i; echo
>>   fi
>> done
>> umount ./loop/mount
>> umount ./loop
>> losetup -d $LOOPDEV
>>
>> Signed-off-by: Andrey Pronin <apronin@xxxxxxxxxxxx>
>> ---
>>
>> Changes since v1:
>>  - Switched to datasync=1 for ecryptfs_fsync_lower() in truncate_upper()\
> 
> It looks like this patch got lost... Can we get it in?

It did get lost. I'll have another look at it and get it into an
upcoming -rc release. Thanks for the reminder!

Tyler

> 
> Thanks!
> 
>>
>>  fs/ecryptfs/ecryptfs_kernel.h |  1 +
>>  fs/ecryptfs/inode.c           |  6 ++++++
>>  fs/ecryptfs/read_write.c      | 22 ++++++++++++++++++++++
>>  3 files changed, 29 insertions(+)
>>
>> diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
>> index f622a733f7ad..567698421270 100644
>> --- a/fs/ecryptfs/ecryptfs_kernel.h
>> +++ b/fs/ecryptfs/ecryptfs_kernel.h
>> @@ -689,6 +689,7 @@ int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
>>                                      pgoff_t page_index,
>>                                      size_t offset_in_page, size_t size,
>>                                      struct inode *ecryptfs_inode);
>> +int ecryptfs_fsync_lower(struct inode *ecryptfs_inode, int datasync);
>>  struct page *ecryptfs_get_locked_page(struct inode *inode, loff_t index);
>>  int ecryptfs_parse_packet_length(unsigned char *data, size_t *size,
>>                                  size_t *length_size);
>> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
>> index 5eab400e2590..a96988ba6928 100644
>> --- a/fs/ecryptfs/inode.c
>> +++ b/fs/ecryptfs/inode.c
>> @@ -827,6 +827,12 @@ static int truncate_upper(struct dentry *dentry, struct iattr *ia,
>>                                "rc = [%d]\n", rc);
>>                         goto out;
>>                 }
>> +               rc = ecryptfs_fsync_lower(inode, 1);
>> +               if (rc) {
>> +                       printk(KERN_WARNING "Problem with ecryptfs_fsync_lower,"
>> +                              "continue without syncing; "
>> +                              "rc = [%d]\n", rc);
>> +               }
>>                 /* We are reducing the size of the ecryptfs file, and need to
>>                  * know if we need to reduce the size of the lower file. */
>>                 lower_size_before_truncate =
>> diff --git a/fs/ecryptfs/read_write.c b/fs/ecryptfs/read_write.c
>> index 09fe622274e4..ba2dd6263875 100644
>> --- a/fs/ecryptfs/read_write.c
>> +++ b/fs/ecryptfs/read_write.c
>> @@ -271,3 +271,25 @@ int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
>>         flush_dcache_page(page_for_ecryptfs);
>>         return rc;
>>  }
>> +
>> +/**
>> + * ecryptfs_fsync_lower
>> + * @ecryptfs_inode: The eCryptfs inode
>> + * @datasync: Only perform a fdatasync operation
>> + *
>> + * Write back data and metadata for the lower file to disk.  If @datasync is
>> + * set only metadata needed to access modified file data is written.
>> + *
>> + * Returns 0 on success; less than zero on error
>> + */
>> +int ecryptfs_fsync_lower(struct inode *ecryptfs_inode, int datasync)
>> +{
>> +       struct file *lower_file;
>> +
>> +       lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
>> +       if (!lower_file)
>> +               return -EIO;
>> +       if (!lower_file->f_op->fsync)
>> +               return 0;
>> +       return vfs_fsync(lower_file, datasync);
>> +}
>> --
>> 2.13.0.rc0.306.g87b477812d-goog
>>
> 
> 
>

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