A secure anonymous file is one we hooked up to its own inode (as opposed to the shared inode we use for non-secure anonymous files). A new selinux hook gives security modules a chance to initialize, label, and veto the creation of these secure anonymous files. Security modules had limit ability to interact with non-secure anonymous files due to all of these files sharing a single inode.
Signed-off-by: Daniel Colascione <dan...@google.com> --- fs/anon_inodes.c | 45 ++++++++++++++++++++++++++++++--------- include/linux/lsm_hooks.h | 8 +++++++ include/linux/security.h | 2 ++ security/security.c | 8 +++++++ 4 files changed, 53 insertions(+), 10 deletions(-) diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c index caa36019afca..d68d76523ad3 100644 --- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -55,6 +55,23 @@ static struct file_system_type anon_inode_fs_type = { .kill_sb = kill_anon_super, }; +struct inode *anon_inode_make_secure_inode(const char *name, + const struct file_operations *fops) +{ + struct inode *inode; + int error; + inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); + if (IS_ERR(inode)) + return ERR_PTR(PTR_ERR(inode)); + inode->i_flags &= ~S_PRIVATE; + error = security_inode_init_security_anon(inode, name, fops); + if (error) { + iput(inode); + return ERR_PTR(error); + } + return inode; +} + /** * anon_inode_getfile2 - creates a new file instance by hooking it up to * an anonymous inode, and a dentry that describe @@ -72,7 +89,9 @@ static struct file_system_type anon_inode_fs_type = { * hence saving memory and avoiding code duplication for the file/inode/dentry * setup. Returns the newly created file* or an error pointer. * - * anon_inode_flags must be zero. + * If anon_inode_flags contains ANON_INODE_SECURE, create a new inode + * and enable security checks for it. Otherwise, attach a new file to + * a singleton placeholder inode with security checks disabled. */ struct file *anon_inode_getfile2(const char *name, const struct file_operations *fops, @@ -81,17 +100,23 @@ struct file *anon_inode_getfile2(const char *name, struct inode *inode; struct file *file; - if (anon_inode_flags) + if (anon_inode_flags & ~ANON_INODE_SECURE) return ERR_PTR(-EINVAL); - inode = anon_inode_inode; - if (IS_ERR(inode)) - return ERR_PTR(-ENODEV); - /* - * We know the anon_inode inode count is always - * greater than zero, so ihold() is safe. - */ - ihold(inode); + if (anon_inode_flags & ANON_INODE_SECURE) { + inode = anon_inode_make_secure_inode(name, fops); + if (IS_ERR(inode)) + return ERR_PTR(PTR_ERR(inode)); + } else { + inode = anon_inode_inode; + if (IS_ERR(inode)) + return ERR_PTR(-ENODEV); + /* + * We know the anon_inode inode count is always + * greater than zero, so ihold() is safe. + */ + ihold(inode); + } if (fops->owner && !try_module_get(fops->owner)) { file = ERR_PTR(-ENOENT); diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index a3763247547c..3744ce9e9172 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -215,6 +215,10 @@ * Returns 0 if @name and @value have been successfully set, * -EOPNOTSUPP if no security attribute is needed, or * -ENOMEM on memory allocation failure. + * @inode_init_security_anon: + * Set up a secure anonymous inode. + * Returns 0 on success. Returns -EPERM if the security module denies + * the creation of this inode. * @inode_create: * Check permission to create a regular file. * @dir contains inode structure of the parent of the new file. @@ -1552,6 +1556,9 @@ union security_list_options { const struct qstr *qstr, const char **name, void **value, size_t *len); + int (*inode_init_security_anon)(struct inode *inode, + const char *name, + const struct file_operations *fops); int (*inode_create)(struct inode *dir, struct dentry *dentry, umode_t mode); int (*inode_link)(struct dentry *old_dentry, struct inode *dir, @@ -1876,6 +1883,7 @@ struct security_hook_heads { struct hlist_head inode_alloc_security; struct hlist_head inode_free_security; struct hlist_head inode_init_security; + struct hlist_head inode_init_security_anon; struct hlist_head inode_create; struct hlist_head inode_link; struct hlist_head inode_unlink; diff --git a/include/linux/security.h b/include/linux/security.h index a8d59d612d27..5b6f7e0de577 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -315,6 +315,8 @@ void security_inode_free(struct inode *inode); int security_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, initxattrs initxattrs, void *fs_data); +int security_inode_init_security_anon(struct inode *inode, const char *name, + const struct file_operations *fops); int security_old_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, const char **name, void **value, size_t *len); diff --git a/security/security.c b/security/security.c index 1bc000f834e2..c87695f66413 100644 --- a/security/security.c +++ b/security/security.c @@ -1001,6 +1001,14 @@ int security_inode_init_security(struct inode *inode, struct inode *dir, } EXPORT_SYMBOL(security_inode_init_security); +int +security_inode_init_security_anon(struct inode *inode, + const char *name, + const struct file_operations *fops) +{ + return call_int_hook(inode_init_security_anon, 0, inode, name, fops); +} + int security_old_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, const char **name, void **value, size_t *len) -- 2.23.0.700.g56cf767bdb-goog