user/sven/linux.git/include/linux/fscrypt.h, branch v5.10.124

fscrypt: add fscrypt_symlink_getattr() for computing st_size

2021-09-08T06:48:59Z

commit d18760560593e5af921f51a8c9b64b6109d634c2 upstream. Add a helper function fscrypt_symlink_getattr() which will be called from the various filesystems' ->getattr() methods to read and decrypt the target of encrypted symlinks in order to report the correct st_size. Detailed explanation: As required by POSIX and as documented in various man pages, st_size for a symlink is supposed to be the length of the symlink target. Unfortunately, st_size has always been wrong for encrypted symlinks because st_size is populated from i_size from disk, which intentionally contains the length of the encrypted symlink target. That's slightly greater than the length of the decrypted symlink target (which is the symlink target that userspace usually sees), and usually won't match the length of the no-key encoded symlink target either. This hadn't been fixed yet because reporting the correct st_size would require reading the symlink target from disk and decrypting or encoding it, which historically has been considered too heavyweight to do in ->getattr(). Also historically, the wrong st_size had only broken a test (LTP lstat03) and there were no known complaints from real users. (This is probably because the st_size of symlinks isn't used too often, and when it is, typically it's for a hint for what buffer size to pass to readlink() -- which a slightly-too-large size still works for.) However, a couple things have changed now. First, there have recently been complaints about the current behavior from real users: - Breakage in rpmbuild: https://github.com/rpm-software-management/rpm/issues/1682 https://github.com/google/fscrypt/issues/305 - Breakage in toybox cpio: https://www.mail-archive.com/toybox@lists.landley.net/msg07193.html - Breakage in libgit2: https://issuetracker.google.com/issues/189629152 (on Android public issue tracker, requires login) Second, we now cache decrypted symlink targets in ->i_link. Therefore, taking the performance hit of reading and decrypting the symlink target in ->getattr() wouldn't be as big a deal as it used to be, since usually it will just save having to do the same thing later. Also note that eCryptfs ended up having to read and decrypt symlink targets in ->getattr() as well, to fix this same issue; see commit 3a60a1686f0d ("eCryptfs: Decrypt symlink target for stat size"). So, let's just bite the bullet, and read and decrypt the symlink target in ->getattr() in order to report the correct st_size. Add a function fscrypt_symlink_getattr() which the filesystems will call to do this. (Alternatively, we could store the decrypted size of symlinks on-disk. But there isn't a great place to do so, and encryption is meant to hide the original size to some extent; that property would be lost.) Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20210702065350.209646-2-ebiggers@kernel.org Signed-off-by: Eric Biggers Signed-off-by: Greg Kroah-Hartman

fscrypt: add fscrypt_is_nokey_name()

2020-12-26T15:02:43Z

commit 159e1de201b6fca10bfec50405a3b53a561096a8 upstream. It's possible to create a duplicate filename in an encrypted directory by creating a file concurrently with adding the encryption key. Specifically, sys_open(O_CREAT) (or sys_mkdir(), sys_mknod(), or sys_symlink()) can lookup the target filename while the directory's encryption key hasn't been added yet, resulting in a negative no-key dentry. The VFS then calls ->create() (or ->mkdir(), ->mknod(), or ->symlink()) because the dentry is negative. Normally, ->create() would return -ENOKEY due to the directory's key being unavailable. However, if the key was added between the dentry lookup and ->create(), then the filesystem will go ahead and try to create the file. If the target filename happens to already exist as a normal name (not a no-key name), a duplicate filename may be added to the directory. In order to fix this, we need to fix the filesystems to prevent ->create(), ->mkdir(), ->mknod(), and ->symlink() on no-key names. (->rename() and ->link() need it too, but those are already handled correctly by fscrypt_prepare_rename() and fscrypt_prepare_link().) In preparation for this, add a helper function fscrypt_is_nokey_name() that filesystems can use to do this check. Use this helper function for the existing checks that fs/crypto/ does for rename and link. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20201118075609.120337-2-ebiggers@kernel.org Signed-off-by: Eric Biggers Signed-off-by: Greg Kroah-Hartman

fscrypt: export fscrypt_d_revalidate()

2020-09-28T21:44:51Z

Dentries that represent no-key names must have a dentry_operations that includes fscrypt_d_revalidate(). Currently, this is handled by fscrypt_prepare_lookup() installing fscrypt_d_ops. However, ceph support for encryption (https://lore.kernel.org/r/20200914191707.380444-1-jlayton@kernel.org) can't use fscrypt_d_ops, since ceph already has its own dentry_operations. Similarly, ext4 and f2fs support for directories that are both encrypted and casefolded (https://lore.kernel.org/r/20200923010151.69506-1-drosen@google.com) can't use fscrypt_d_ops either, since casefolding requires some dentry operations too. To satisfy both users, we need to move the responsibility of installing the dentry_operations to filesystems. In preparation for this, export fscrypt_d_revalidate() and give it a !CONFIG_FS_ENCRYPTION stub. Reviewed-by: Jeff Layton Link: https://lore.kernel.org/r/20200924054721.187797-1-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: rename DCACHE_ENCRYPTED_NAME to DCACHE_NOKEY_NAME

2020-09-24T04:29:49Z

Originally we used the term "encrypted name" or "ciphertext name" to mean the encoded filename that is shown when an encrypted directory is listed without its key. But these terms are ambiguous since they also mean the filename stored on-disk. "Encrypted name" is especially ambiguous since it could also be understood to mean "this filename is encrypted on-disk", similar to "encrypted file". So we've started calling these encoded names "no-key names" instead. Therefore, rename DCACHE_ENCRYPTED_NAME to DCACHE_NOKEY_NAME to avoid confusion about what this flag means. Link: https://lore.kernel.org/r/20200924042624.98439-3-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: don't call no-key names "ciphertext names"

2020-09-24T04:29:49Z

Currently we're using the term "ciphertext name" ambiguously because it can mean either the actual ciphertext filename, or the encoded filename that is shown when an encrypted directory is listed without its key. The latter we're now usually calling the "no-key name"; and while it's derived from the ciphertext name, it's not the same thing. To avoid this ambiguity, rename fscrypt_name::is_ciphertext_name to fscrypt_name::is_nokey_name, and update comments that say "ciphertext name" (or "encrypted name") to say "no-key name" instead when warranted. Link: https://lore.kernel.org/r/20200924042624.98439-2-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: make fscrypt_set_test_dummy_encryption() take a 'const char *'

2020-09-22T13:48:52Z

fscrypt_set_test_dummy_encryption() requires that the optional argument to the test_dummy_encryption mount option be specified as a substring_t. That doesn't work well with filesystems that use the new mount API, since the new way of parsing mount options doesn't use substring_t. Make it take the argument as a 'const char *' instead. Instead of moving the match_strdup() into the callers in ext4 and f2fs, make them just use arg->from directly. Since the pattern is "test_dummy_encryption=%s", the argument will be null-terminated. Acked-by: Jeff Layton Link: https://lore.kernel.org/r/20200917041136.178600-14-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: handle test_dummy_encryption in more logical way

2020-09-22T13:48:49Z

The behavior of the test_dummy_encryption mount option is that when a new file (or directory or symlink) is created in an unencrypted directory, it's automatically encrypted using a dummy encryption policy. That's it; in particular, the encryption (or lack thereof) of existing files (or directories or symlinks) doesn't change. Unfortunately the implementation of test_dummy_encryption is a bit weird and confusing. When test_dummy_encryption is enabled and a file is being created in an unencrypted directory, we set up an encryption key (->i_crypt_info) for the directory. This isn't actually used to do any encryption, however, since the directory is still unencrypted! Instead, ->i_crypt_info is only used for inheriting the encryption policy. One consequence of this is that the filesystem ends up providing a "dummy context" (policy + nonce) instead of a "dummy policy". In commit ed318a6cc0b6 ("fscrypt: support test_dummy_encryption=v2"), I mistakenly thought this was required. However, actually the nonce only ends up being used to derive a key that is never used. Another consequence of this implementation is that it allows for 'inode->i_crypt_info != NULL && !IS_ENCRYPTED(inode)', which is an edge case that can be forgotten about. For example, currently FS_IOC_GET_ENCRYPTION_POLICY on an unencrypted directory may return the dummy encryption policy when the filesystem is mounted with test_dummy_encryption. That seems like the wrong thing to do, since again, the directory itself is not actually encrypted. Therefore, switch to a more logical and maintainable implementation where the dummy encryption policy inheritance is done without setting up keys for unencrypted directories. This involves: - Adding a function fscrypt_policy_to_inherit() which returns the encryption policy to inherit from a directory. This can be a real policy, a dummy policy, or no policy. - Replacing struct fscrypt_dummy_context, ->get_dummy_context(), etc. with struct fscrypt_dummy_policy, ->get_dummy_policy(), etc. - Making fscrypt_fname_encrypted_size() take an fscrypt_policy instead of an inode. Acked-by: Jaegeuk Kim Acked-by: Jeff Layton Link: https://lore.kernel.org/r/20200917041136.178600-13-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: move fscrypt_prepare_symlink() out-of-line

2020-09-22T13:48:47Z

In preparation for moving the logic for "get the encryption policy inherited by new files in this directory" to a single place, make fscrypt_prepare_symlink() a regular function rather than an inline function that wraps __fscrypt_prepare_symlink(). This way, the new function fscrypt_policy_to_inherit() won't need to be exported to filesystems. Acked-by: Jeff Layton Link: https://lore.kernel.org/r/20200917041136.178600-12-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: remove fscrypt_inherit_context()

2020-09-22T13:48:39Z

Now that all filesystems have been converted to use fscrypt_prepare_new_inode() and fscrypt_set_context(), fscrypt_inherit_context() is no longer used. Remove it. Acked-by: Jeff Layton Link: https://lore.kernel.org/r/20200917041136.178600-8-ebiggers@kernel.org Signed-off-by: Eric Biggers

fscrypt: add fscrypt_prepare_new_inode() and fscrypt_set_context()

2020-09-22T13:48:29Z

fscrypt_get_encryption_info() is intended to be GFP_NOFS-safe. But actually it isn't, since it uses functions like crypto_alloc_skcipher() which aren't GFP_NOFS-safe, even when called under memalloc_nofs_save(). Therefore it can deadlock when called from a context that needs GFP_NOFS, e.g. during an ext4 transaction or between f2fs_lock_op() and f2fs_unlock_op(). This happens when creating a new encrypted file. We can't fix this by just not setting up the key for new inodes right away, since new symlinks need their key to encrypt the symlink target. So we need to set up the new inode's key before starting the transaction. But just calling fscrypt_get_encryption_info() earlier doesn't work, since it assumes the encryption context is already set, and the encryption context can't be set until the transaction. The recently proposed fscrypt support for the ceph filesystem (https://lkml.kernel.org/linux-fscrypt/20200821182813.52570-1-jlayton@kernel.org/T/#u) will have this same ordering problem too, since ceph will need to encrypt new symlinks before setting their encryption context. Finally, f2fs can deadlock when the filesystem is mounted with '-o test_dummy_encryption' and a new file is created in an existing unencrypted directory. Similarly, this is caused by holding too many locks when calling fscrypt_get_encryption_info(). To solve all these problems, add new helper functions: - fscrypt_prepare_new_inode() sets up a new inode's encryption key (fscrypt_info), using the parent directory's encryption policy and a new random nonce. It neither reads nor writes the encryption context. - fscrypt_set_context() persists the encryption context of a new inode, using the information from the fscrypt_info already in memory. This replaces fscrypt_inherit_context(). Temporarily keep fscrypt_inherit_context() around until all filesystems have been converted to use fscrypt_set_context(). Acked-by: Jeff Layton Link: https://lore.kernel.org/r/20200917041136.178600-2-ebiggers@kernel.org Signed-off-by: Eric Biggers