fscrypt: allow deleting files with unsupported encryption policy
Currently it's impossible to delete files that use an unsupported
encryption policy, as the kernel will just return an error when
performing any operation on the top-level encrypted directory, even just
a path lookup into the directory or opening the directory for readdir.
More specifically, this occurs in any of the following cases:
- The encryption context has an unrecognized version number. Current
kernels know about v1 and v2, but there could be more versions in the
future.
- The encryption context has unrecognized encryption modes
(FSCRYPT_MODE_*) or flags (FSCRYPT_POLICY_FLAG_*), an unrecognized
combination of modes, or reserved bits set.
- The encryption key has been added and the encryption modes are
recognized but aren't available in the crypto API -- for example, a
directory is encrypted with FSCRYPT_MODE_ADIANTUM but the kernel
doesn't have CONFIG_CRYPTO_ADIANTUM enabled.
It's desirable to return errors for most operations on files that use an
unsupported encryption policy, but the current behavior is too strict.
We need to allow enough to delete files, so that people can't be stuck
with undeletable files when downgrading kernel versions. That includes
allowing directories to be listed and allowing dentries to be looked up.
Fix this by modifying the key setup logic to treat an unsupported
encryption policy in the same way as "key unavailable" in the cases that
are required for a recursive delete to work: preparing for a readdir or
a dentry lookup, revalidating a dentry, or checking whether an inode has
the same encryption policy as its parent directory.
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/20201203022041.230976-10-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 1fbe6c2..988dadf 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -404,7 +404,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
fname->disk_name.len = iname->len;
return 0;
}
- ret = fscrypt_get_encryption_info(dir);
+ ret = fscrypt_get_encryption_info(dir, lookup);
if (ret)
return ret;
@@ -560,7 +560,11 @@ int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
return -ECHILD;
dir = dget_parent(dentry);
- err = fscrypt_get_encryption_info(d_inode(dir));
+ /*
+ * Pass allow_unsupported=true, so that files with an unsupported
+ * encryption policy can be deleted.
+ */
+ err = fscrypt_get_encryption_info(d_inode(dir), true);
valid = !fscrypt_has_encryption_key(d_inode(dir));
dput(dir);
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index c1c3026..f0bed6b 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -571,7 +571,7 @@ int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
void fscrypt_hash_inode_number(struct fscrypt_info *ci,
const struct fscrypt_master_key *mk);
-int fscrypt_get_encryption_info(struct inode *inode);
+int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported);
/**
* fscrypt_require_key() - require an inode's encryption key
@@ -589,7 +589,7 @@ int fscrypt_get_encryption_info(struct inode *inode);
static inline int fscrypt_require_key(struct inode *inode)
{
if (IS_ENCRYPTED(inode)) {
- int err = fscrypt_get_encryption_info(inode);
+ int err = fscrypt_get_encryption_info(inode, false);
if (err)
return err;
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 1c16dba..79570e0 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -116,7 +116,7 @@ EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
int __fscrypt_prepare_readdir(struct inode *dir)
{
- return fscrypt_get_encryption_info(dir);
+ return fscrypt_get_encryption_info(dir, true);
}
EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
@@ -332,7 +332,7 @@ const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
* Try to set up the symlink's encryption key, but we can continue
* regardless of whether the key is available or not.
*/
- err = fscrypt_get_encryption_info(inode);
+ err = fscrypt_get_encryption_info(inode, false);
if (err)
return ERR_PTR(err);
has_key = fscrypt_has_encryption_key(inode);
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 6339b30..261293f 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -546,6 +546,11 @@ fscrypt_setup_encryption_info(struct inode *inode,
/**
* fscrypt_get_encryption_info() - set up an inode's encryption key
* @inode: the inode to set up the key for. Must be encrypted.
+ * @allow_unsupported: if %true, treat an unsupported encryption policy (or
+ * unrecognized encryption context) the same way as the key
+ * being unavailable, instead of returning an error. Use
+ * %false unless the operation being performed is needed in
+ * order for files (or directories) to be deleted.
*
* Set up ->i_crypt_info, if it hasn't already been done.
*
@@ -556,7 +561,7 @@ fscrypt_setup_encryption_info(struct inode *inode,
* encryption key is unavailable. (Use fscrypt_has_encryption_key() to
* distinguish these cases.) Also can return another -errno code.
*/
-int fscrypt_get_encryption_info(struct inode *inode)
+int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
{
int res;
union fscrypt_context ctx;
@@ -567,24 +572,34 @@ int fscrypt_get_encryption_info(struct inode *inode)
res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
if (res < 0) {
+ if (res == -ERANGE && allow_unsupported)
+ return 0;
fscrypt_warn(inode, "Error %d getting encryption context", res);
return res;
}
res = fscrypt_policy_from_context(&policy, &ctx, res);
if (res) {
+ if (allow_unsupported)
+ return 0;
fscrypt_warn(inode,
"Unrecognized or corrupt encryption context");
return res;
}
- if (!fscrypt_supported_policy(&policy, inode))
+ if (!fscrypt_supported_policy(&policy, inode)) {
+ if (allow_unsupported)
+ return 0;
return -EINVAL;
+ }
res = fscrypt_setup_encryption_info(inode, &policy,
fscrypt_context_nonce(&ctx),
IS_CASEFOLDED(inode) &&
S_ISDIR(inode->i_mode));
+
+ if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
+ res = 0;
if (res == -ENOKEY)
res = 0;
return res;
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index faa0f21..a51cef6 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -590,7 +590,7 @@ EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_nonce);
int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
{
union fscrypt_policy parent_policy, child_policy;
- int err;
+ int err, err1, err2;
/* No restrictions on file types which are never encrypted */
if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) &&
@@ -620,19 +620,25 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child)
* In any case, if an unexpected error occurs, fall back to "forbidden".
*/
- err = fscrypt_get_encryption_info(parent);
+ err = fscrypt_get_encryption_info(parent, true);
if (err)
return 0;
- err = fscrypt_get_encryption_info(child);
+ err = fscrypt_get_encryption_info(child, true);
if (err)
return 0;
- err = fscrypt_get_policy(parent, &parent_policy);
- if (err)
- return 0;
+ err1 = fscrypt_get_policy(parent, &parent_policy);
+ err2 = fscrypt_get_policy(child, &child_policy);
- err = fscrypt_get_policy(child, &child_policy);
- if (err)
+ /*
+ * Allow the case where the parent and child both have an unrecognized
+ * encryption policy, so that files with an unrecognized encryption
+ * policy can be deleted.
+ */
+ if (err1 == -EINVAL && err2 == -EINVAL)
+ return 1;
+
+ if (err1 || err2)
return 0;
return fscrypt_policies_equal(&parent_policy, &child_policy);