linux-kernel - Re: [PATCH v3 0/3] ceph: fscrypt: fix atomic open bug for encrypted directories

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Date:   Mon, 20 Mar 2023 14:07:10 +0000
From:   Luís Henriques <lhenriques@...e.de>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        Jeff Layton <jlayton@...nel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        linux-fscrypt@...r.kernel.org, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/3] ceph: fscrypt: fix atomic open bug for encrypted
 directories

Xiubo Li <xiubli@...hat.com> writes:

> On 17/03/2023 02:14, Luís Henriques wrote:
>> Hi!
>>
>> I started seeing fstest generic/123 failing in ceph fscrypt, when running it
>> with 'test_dummy_encryption'.  This test is quite simple:
>>
>> 1. Creates a directory with write permissions for root only
>> 2. Writes into a file in that directory
>> 3. Uses 'su' to try to modify that file as a different user, and
>>     gets -EPERM
>>
>> All the test steps succeed, but the test fails to cleanup: 'rm -rf <dir>'
>> will fail with -ENOTEMPTY.  'strace' shows that calling unlinkat() to remove
>> the file got a -ENOENT and then -ENOTEMPTY for the directory.
>>
>> This is because 'su' does a drop_caches ('su (874): drop_caches: 2' in
>> dmesg), and ceph's atomic open will do:
>>
>> 	if (IS_ENCRYPTED(dir)) {
>> 		set_bit(CEPH_MDS_R_FSCRYPT_FILE, &req->r_req_flags);
>> 		if (!fscrypt_has_encryption_key(dir)) {
>> 			spin_lock(&dentry->d_lock);
>> 			dentry->d_flags |= DCACHE_NOKEY_NAME;
>> 			spin_unlock(&dentry->d_lock);
>> 		}
>> 	}
>>
>> Although 'dir' has the encryption key available, fscrypt_has_encryption_key()
>> will return 'false' because fscrypt info isn't yet set after the cache
>> cleanup.
>>
>> The first patch will add a new helper for the atomic_open that will force
>> the fscrypt info to be loaded into an inode that has been evicted recently
>> but for which the key is still available.
>>
>> The second patch switches ceph atomic_open to use the new fscrypt helper.
>>
>> Cheers,
>> --
>> Luís
>>
>> Changes since v2:
>> - Make helper more generic and to be used both in lookup and atomic open
>>    operations
>> - Modify ceph_lookup (patch 0002) and ceph_atomic_open (patch 0003) to use
>>    the new helper
>>
>> Changes since v1:
>> - Dropped IS_ENCRYPTED() from helper function because kerneldoc says
>>    already that it applies to encrypted directories and, most importantly,
>>    because it would introduce a different behaviour for
>>    CONFIG_FS_ENCRYPTION and !CONFIG_FS_ENCRYPTION.
>> - Rephrased helper kerneldoc
>>
>> Changes since initial RFC (after Eric's review):
>> - Added kerneldoc comments to the new fscrypt helper
>> - Dropped '__' from helper name (now fscrypt_prepare_atomic_open())
>> - Added IS_ENCRYPTED() check in helper
>> - DCACHE_NOKEY_NAME is not set if fscrypt_get_encryption_info() returns an
>>    error
>> - Fixed helper for !CONFIG_FS_ENCRYPTION (now defined 'static inline')
>
> This series looks good to me.
>
> And I have run the test locally and worked well.

Awesome, thanks a lot Xiubo.  I've been testing it locally as well and I
haven't observed any breakage either.

Cheers,
-- 
Luís