diff options
| -rw-r--r-- | fs/crypto/policy.c | 87 |
1 files changed, 68 insertions, 19 deletions
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c index d71ec3780d0c..210976e7a269 100644 --- a/fs/crypto/policy.c +++ b/fs/crypto/policy.c @@ -137,27 +137,61 @@ int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg) } EXPORT_SYMBOL(fscrypt_ioctl_get_policy); +/** + * fscrypt_has_permitted_context() - is a file's encryption policy permitted + * within its directory? + * + * @parent: inode for parent directory + * @child: inode for file being looked up, opened, or linked into @parent + * + * Filesystems must call this before permitting access to an inode in a + * situation where the parent directory is encrypted (either before allowing + * ->lookup() to succeed, or for a regular file before allowing it to be opened) + * and before any operation that involves linking an inode into an encrypted + * directory, including link, rename, and cross rename. It enforces the + * constraint that within a given encrypted directory tree, all files use the + * same encryption policy. The pre-access check is needed to detect potentially + * malicious offline violations of this constraint, while the link and rename + * checks are needed to prevent online violations of this constraint. + * + * Return: 1 if permitted, 0 if forbidden. If forbidden, the caller must fail + * the filesystem operation with EPERM. + */ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child) { - struct fscrypt_info *parent_ci, *child_ci; + const struct fscrypt_operations *cops = parent->i_sb->s_cop; + const struct fscrypt_info *parent_ci, *child_ci; + struct fscrypt_context parent_ctx, child_ctx; int res; - if ((parent == NULL) || (child == NULL)) { - printk(KERN_ERR "parent %p child %p\n", parent, child); - BUG_ON(1); - } - /* No restrictions on file types which are never encrypted */ if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) && !S_ISLNK(child->i_mode)) return 1; - /* no restrictions if the parent directory is not encrypted */ - if (!parent->i_sb->s_cop->is_encrypted(parent)) + /* No restrictions if the parent directory is unencrypted */ + if (!cops->is_encrypted(parent)) return 1; - /* if the child directory is not encrypted, this is always a problem */ - if (!parent->i_sb->s_cop->is_encrypted(child)) + + /* Encrypted directories must not contain unencrypted files */ + if (!cops->is_encrypted(child)) return 0; + + /* + * Both parent and child are encrypted, so verify they use the same + * encryption policy. Compare the fscrypt_info structs if the keys are + * available, otherwise retrieve and compare the fscrypt_contexts. + * + * Note that the fscrypt_context retrieval will be required frequently + * when accessing an encrypted directory tree without the key. + * Performance-wise this is not a big deal because we already don't + * really optimize for file access without the key (to the extent that + * such access is even possible), given that any attempted access + * already causes a fscrypt_context retrieval and keyring search. + * + * In any case, if an unexpected error occurs, fall back to "forbidden". + */ + res = fscrypt_get_encryption_info(parent); if (res) return 0; @@ -166,17 +200,32 @@ int fscrypt_has_permitted_context(struct inode *parent, struct inode *child) return 0; parent_ci = parent->i_crypt_info; child_ci = child->i_crypt_info; - if (!parent_ci && !child_ci) - return 1; - if (!parent_ci || !child_ci) + + if (parent_ci && child_ci) { + return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key, + FS_KEY_DESCRIPTOR_SIZE) == 0 && + (parent_ci->ci_data_mode == child_ci->ci_data_mode) && + (parent_ci->ci_filename_mode == + child_ci->ci_filename_mode) && + (parent_ci->ci_flags == child_ci->ci_flags); + } + + res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx)); + if (res != sizeof(parent_ctx)) + return 0; + + res = cops->get_context(child, &child_ctx, sizeof(child_ctx)); + if (res != sizeof(child_ctx)) return 0; - return (memcmp(parent_ci->ci_master_key, - child_ci->ci_master_key, - FS_KEY_DESCRIPTOR_SIZE) == 0 && - (parent_ci->ci_data_mode == child_ci->ci_data_mode) && - (parent_ci->ci_filename_mode == child_ci->ci_filename_mode) && - (parent_ci->ci_flags == child_ci->ci_flags)); + return memcmp(parent_ctx.master_key_descriptor, + child_ctx.master_key_descriptor, + FS_KEY_DESCRIPTOR_SIZE) == 0 && + (parent_ctx.contents_encryption_mode == + child_ctx.contents_encryption_mode) && + (parent_ctx.filenames_encryption_mode == + child_ctx.filenames_encryption_mode) && + (parent_ctx.flags == child_ctx.flags); } EXPORT_SYMBOL(fscrypt_has_permitted_context); |