Re: [PATCH 0/2] ceph: fscrypt: fix atomic open bug for encrypted directories

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2023-03-13 at 12:33 +0000, 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 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')
> 
> Luís Henriques (2):
>   fscrypt: new helper function - fscrypt_prepare_atomic_open()
>   ceph: switch atomic open to use new fscrypt helper
> 
>  fs/ceph/file.c          |  8 +++-----
>  fs/crypto/hooks.c       | 35 +++++++++++++++++++++++++++++++++++
>  include/linux/fscrypt.h |  7 +++++++
>  3 files changed, 45 insertions(+), 5 deletions(-)
> 

Looks like a nice cleanup.

Reviewed-by: Jeff Layton <jlayton@kernel.org>