| Message ID | 20200827063522.2563293-2-lokeshgidra@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | SELinux support for anonymous inodes and UFFD | expand |
On Wed, Aug 26, 2020 at 11:35:20PM -0700, Lokesh Gidra wrote: > From: Daniel Colascione <dancol@google.com> > > This change adds a new function, anon_inode_getfd_secure, that creates > anonymous-node file with individual non-S_PRIVATE inode to which security > modules can apply policy. Existing callers continue using the original > singleton-inode kind of anonymous-inode file. We can transition anonymous > inode users to the new kind of anonymous inode in individual patches for > the sake of bisection and review. > > The new function accepts an optional context_inode parameter that > callers can use to provide additional contextual information to > security modules for granting/denying permission to create an anon inode > of the same type. > > For example, in case of userfaultfd, the created inode is a > 'logical child' of the context_inode (userfaultfd inode of the > parent process) in the sense that it provides the security context > required during creation of the child process' userfaultfd inode. > > Signed-off-by: Daniel Colascione <dancol@google.com> > > [Fix comment documenting return values of inode_init_security_anon()] > [Add context_inode description in comments to anon_inode_getfd_secure()] > [Remove definition of anon_inode_getfile_secure() as there are no callers] > [Make _anon_inode_getfile() static] > [Use correct error cast in _anon_inode_getfile()] > [Fix error handling in _anon_inode_getfile()] > > Signed-off-by: Lokesh Gidra <lokeshgidra@google.com> > --- > fs/anon_inodes.c | 147 +++++++++++++++++++++++++--------- > include/linux/anon_inodes.h | 8 ++ > include/linux/lsm_hook_defs.h | 2 + > include/linux/lsm_hooks.h | 9 +++ > include/linux/security.h | 10 +++ > security/security.c | 8 ++ > 6 files changed, 144 insertions(+), 40 deletions(-) > > diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c > index 89714308c25b..c3f16deda211 100644 > --- a/fs/anon_inodes.c > +++ b/fs/anon_inodes.c > @@ -55,61 +55,79 @@ static struct file_system_type anon_inode_fs_type = { > .kill_sb = kill_anon_super, > }; > > -/** > - * anon_inode_getfile - creates a new file instance by hooking it up to an > - * anonymous inode, and a dentry that describe the "class" > - * of the file > - * > - * @name: [in] name of the "class" of the new file > - * @fops: [in] file operations for the new file > - * @priv: [in] private data for the new file (will be file's private_data) > - * @flags: [in] flags > - * > - * Creates a new file by hooking it on a single inode. This is useful for files > - * that do not need to have a full-fledged inode in order to operate correctly. > - * All the files created with anon_inode_getfile() will share a single inode, > - * hence saving memory and avoiding code duplication for the file/inode/dentry > - * setup. Returns the newly created file* or an error pointer. > - */ > -struct file *anon_inode_getfile(const char *name, > - const struct file_operations *fops, > - void *priv, int flags) > +static struct inode *anon_inode_make_secure_inode( > + const char *name, > + const struct inode *context_inode) > { > - struct file *file; > + struct inode *inode; > + const struct qstr qname = QSTR_INIT(name, strlen(name)); > + int error; > + > + inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); > + if (IS_ERR(inode)) > + return inode; > + inode->i_flags &= ~S_PRIVATE; > + error = security_inode_init_security_anon(inode, &qname, context_inode); > + if (error) { > + iput(inode); > + return ERR_PTR(error); > + } > + return inode; > +} Hey, Iiuc, this makes each newly created anon inode fd correspond to a unique file and to a unique inode: fd1 -> file1 -> inode1 fd2 -> file2 -> inode2 Whereas before we had every anon inode fd correspond to a unique file but all files map to the _same_ inode: fd1 -> file1 -> inode fd2 -> file2 -> inode The old behavior of hooking up a each anon inode fd to the same inode prevented having an evict method attached to the inode. Because it was shared that wasn't possible but also simply because that inode never got evicted anyway. That surely was intended but it's a bummer to some extent. With the new model you also can't have an evict method because now you have a separate inode for each file. I'm probably going to get killed for suggesting this but: If we're going to expand the anonymous inode infrastructure anyway is there a way we can make it so that we have a way to allocate a single inode for multiple anonymous inode fds and have callers opt-in to this behavior. We'd need a way to find this inode again, obviously. This would allow for some features on top of anonymous inode fds that can refer to the same object, i.e. anonymous inode fds that currently stash away the same object in f->private_data. In such a model we could allow such anonymous inode fds to stash away objects in inode->i_private instead of f->private_data and attach an evict method to it. This would e.g. allow a process to be killed when the last pidfd to it is closed or a seccomp notifier fd to notify when the filter is released without having to do separate reference counting. This would need a way to lookup that inode by the object that is stashed away in it of course which could probably be done by an idr or an xarray or something cleverer. It would obviously only affect a subset of anonymous inode fds so any other anonymous inode fds wouldn't be impacted since they can still use the single-anon-inode interface. Christian
On Tue, Sep 1, 2020 at 5:41 AM Christian Brauner <christian.brauner@ubuntu.com> wrote: > > On Wed, Aug 26, 2020 at 11:35:20PM -0700, Lokesh Gidra wrote: > > From: Daniel Colascione <dancol@google.com> > > > > This change adds a new function, anon_inode_getfd_secure, that creates > > anonymous-node file with individual non-S_PRIVATE inode to which security > > modules can apply policy. Existing callers continue using the original > > singleton-inode kind of anonymous-inode file. We can transition anonymous > > inode users to the new kind of anonymous inode in individual patches for > > the sake of bisection and review. > > > > The new function accepts an optional context_inode parameter that > > callers can use to provide additional contextual information to > > security modules for granting/denying permission to create an anon inode > > of the same type. > > > > For example, in case of userfaultfd, the created inode is a > > 'logical child' of the context_inode (userfaultfd inode of the > > parent process) in the sense that it provides the security context > > required during creation of the child process' userfaultfd inode. > > > > Signed-off-by: Daniel Colascione <dancol@google.com> > > > > [Fix comment documenting return values of inode_init_security_anon()] > > [Add context_inode description in comments to anon_inode_getfd_secure()] > > [Remove definition of anon_inode_getfile_secure() as there are no callers] > > [Make _anon_inode_getfile() static] > > [Use correct error cast in _anon_inode_getfile()] > > [Fix error handling in _anon_inode_getfile()] > > > > Signed-off-by: Lokesh Gidra <lokeshgidra@google.com> > > --- > > fs/anon_inodes.c | 147 +++++++++++++++++++++++++--------- > > include/linux/anon_inodes.h | 8 ++ > > include/linux/lsm_hook_defs.h | 2 + > > include/linux/lsm_hooks.h | 9 +++ > > include/linux/security.h | 10 +++ > > security/security.c | 8 ++ > > 6 files changed, 144 insertions(+), 40 deletions(-) > > > > diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c > > index 89714308c25b..c3f16deda211 100644 > > --- a/fs/anon_inodes.c > > +++ b/fs/anon_inodes.c > > @@ -55,61 +55,79 @@ static struct file_system_type anon_inode_fs_type = { > > .kill_sb = kill_anon_super, > > }; > > > > -/** > > - * anon_inode_getfile - creates a new file instance by hooking it up to an > > - * anonymous inode, and a dentry that describe the "class" > > - * of the file > > - * > > - * @name: [in] name of the "class" of the new file > > - * @fops: [in] file operations for the new file > > - * @priv: [in] private data for the new file (will be file's private_data) > > - * @flags: [in] flags > > - * > > - * Creates a new file by hooking it on a single inode. This is useful for files > > - * that do not need to have a full-fledged inode in order to operate correctly. > > - * All the files created with anon_inode_getfile() will share a single inode, > > - * hence saving memory and avoiding code duplication for the file/inode/dentry > > - * setup. Returns the newly created file* or an error pointer. > > - */ > > -struct file *anon_inode_getfile(const char *name, > > - const struct file_operations *fops, > > - void *priv, int flags) > > +static struct inode *anon_inode_make_secure_inode( > > + const char *name, > > + const struct inode *context_inode) > > { > > - struct file *file; > > + struct inode *inode; > > + const struct qstr qname = QSTR_INIT(name, strlen(name)); > > + int error; > > + > > + inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); > > + if (IS_ERR(inode)) > > + return inode; > > + inode->i_flags &= ~S_PRIVATE; > > + error = security_inode_init_security_anon(inode, &qname, context_inode); > > + if (error) { > > + iput(inode); > > + return ERR_PTR(error); > > + } > > + return inode; > > +} > > Hey, > > Iiuc, this makes each newly created anon inode fd correspond to a unique > file and to a unique inode: > > fd1 -> file1 -> inode1 > fd2 -> file2 -> inode2 > Not every anon inode. Just the ones created through anon_inode_getfd_secure() API. > Whereas before we had every anon inode fd correspond to a unique file > but all files map to the _same_ inode: > > fd1 -> file1 -> inode > fd2 -> file2 -> inode > Thils is still the case if anon_inode_getfile() and/or anon_inode_getfd() APIs are used. > The old behavior of hooking up a each anon inode fd to the same inode > prevented having an evict method attached to the inode. Because it was > shared that wasn't possible but also simply because that inode never got > evicted anyway. That surely was intended but it's a bummer to some > extent. > With the new model you also can't have an evict method because now you > have a separate inode for each file. > > I'm probably going to get killed for suggesting this but: > If we're going to expand the anonymous inode infrastructure anyway is > there a way we can make it so that we have a way to allocate a single > inode for multiple anonymous inode fds and have callers opt-in to this > behavior. We'd need a way to find this inode again, obviously. > > This would allow for some features on top of anonymous inode fds that > can refer to the same object, i.e. anonymous inode fds that currently > stash away the same object in f->private_data. > In such a model we could allow such anonymous inode fds to stash away > objects in inode->i_private instead of f->private_data and attach an > evict method to it. This would e.g. allow a process to be killed when > the last pidfd to it is closed or a seccomp notifier fd to notify when > the filter is released without having to do separate reference counting. > I didn't fully understand the example you gave and the role that evict method will play in it. Can you please elaborate a bit more. But, I'd like to point you to a previous discussion between Daniel Colascione (the original contributor of this patch series) and Stephan Smalley on the topic of inodes https://lore.kernel.org/lkml/CAKOZuesUVSYJ6EjHFL3QyiWKVmyhm1fLp5Bm_SHjB3_s1gn08A@mail.gmail.com/ I agree with Daniel (see his replies in the thread link above) that a separate inode per anon inode fd keeps the design simple, particularly from the security context perspective. > This would need a way to lookup that inode by the object that is stashed > away in it of course which could probably be done by an idr or an > xarray or something cleverer. It would obviously only affect a subset of > anonymous inode fds so any other anonymous inode fds wouldn't be > impacted since they can still use the single-anon-inode interface. > > Christian
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c index 89714308c25b..c3f16deda211 100644 --- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -55,61 +55,79 @@ static struct file_system_type anon_inode_fs_type = { .kill_sb = kill_anon_super, }; -/** - * anon_inode_getfile - creates a new file instance by hooking it up to an - * anonymous inode, and a dentry that describe the "class" - * of the file - * - * @name: [in] name of the "class" of the new file - * @fops: [in] file operations for the new file - * @priv: [in] private data for the new file (will be file's private_data) - * @flags: [in] flags - * - * Creates a new file by hooking it on a single inode. This is useful for files - * that do not need to have a full-fledged inode in order to operate correctly. - * All the files created with anon_inode_getfile() will share a single inode, - * hence saving memory and avoiding code duplication for the file/inode/dentry - * setup. Returns the newly created file* or an error pointer. - */ -struct file *anon_inode_getfile(const char *name, - const struct file_operations *fops, - void *priv, int flags) +static struct inode *anon_inode_make_secure_inode( + const char *name, + const struct inode *context_inode) { - struct file *file; + struct inode *inode; + const struct qstr qname = QSTR_INIT(name, strlen(name)); + int error; + + inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); + if (IS_ERR(inode)) + return inode; + inode->i_flags &= ~S_PRIVATE; + error = security_inode_init_security_anon(inode, &qname, context_inode); + if (error) { + iput(inode); + return ERR_PTR(error); + } + return inode; +} - if (IS_ERR(anon_inode_inode)) - return ERR_PTR(-ENODEV); +static struct file *_anon_inode_getfile(const char *name, + const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode, + bool secure) +{ + struct inode *inode; + struct file *file; if (fops->owner && !try_module_get(fops->owner)) return ERR_PTR(-ENOENT); - /* - * We know the anon_inode inode count is always greater than zero, - * so ihold() is safe. - */ - ihold(anon_inode_inode); - file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name, + if (secure) { + inode = anon_inode_make_secure_inode(name, context_inode); + if (IS_ERR(inode)) { + file = ERR_CAST(inode); + goto err; + } + } else { + inode = anon_inode_inode; + if (IS_ERR(inode)) { + file = ERR_PTR(-ENODEV); + goto err; + } + /* + * We know the anon_inode inode count is always + * greater than zero, so ihold() is safe. + */ + ihold(inode); + } + + file = alloc_file_pseudo(inode, anon_inode_mnt, name, flags & (O_ACCMODE | O_NONBLOCK), fops); if (IS_ERR(file)) - goto err; + goto err_iput; - file->f_mapping = anon_inode_inode->i_mapping; + file->f_mapping = inode->i_mapping; file->private_data = priv; return file; +err_iput: + iput(inode); err: - iput(anon_inode_inode); module_put(fops->owner); return file; } -EXPORT_SYMBOL_GPL(anon_inode_getfile); /** - * anon_inode_getfd - creates a new file instance by hooking it up to an - * anonymous inode, and a dentry that describe the "class" - * of the file + * anon_inode_getfile - creates a new file instance by hooking it up to an + * anonymous inode, and a dentry that describe the "class" + * of the file * * @name: [in] name of the "class" of the new file * @fops: [in] file operations for the new file @@ -118,12 +136,23 @@ EXPORT_SYMBOL_GPL(anon_inode_getfile); * * Creates a new file by hooking it on a single inode. This is useful for files * that do not need to have a full-fledged inode in order to operate correctly. - * All the files created with anon_inode_getfd() will share a single inode, + * All the files created with anon_inode_getfile() will share a single inode, * hence saving memory and avoiding code duplication for the file/inode/dentry - * setup. Returns new descriptor or an error code. + * setup. Returns the newly created file* or an error pointer. */ -int anon_inode_getfd(const char *name, const struct file_operations *fops, - void *priv, int flags) +struct file *anon_inode_getfile(const char *name, + const struct file_operations *fops, + void *priv, int flags) +{ + return _anon_inode_getfile(name, fops, priv, flags, NULL, false); +} +EXPORT_SYMBOL_GPL(anon_inode_getfile); + +static int _anon_inode_getfd(const char *name, + const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode, + bool secure) { int error, fd; struct file *file; @@ -133,7 +162,8 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops, return error; fd = error; - file = anon_inode_getfile(name, fops, priv, flags); + file = _anon_inode_getfile(name, fops, priv, flags, context_inode, + secure); if (IS_ERR(file)) { error = PTR_ERR(file); goto err_put_unused_fd; @@ -146,8 +176,45 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops, put_unused_fd(fd); return error; } + +/** + * anon_inode_getfd - creates a new file instance by hooking it up to + * an anonymous inode and a dentry that describe + * the "class" of the file + * + * @name: [in] name of the "class" of the new file + * @fops: [in] file operations for the new file + * @priv: [in] private data for the new file (will be file's private_data) + * @flags: [in] flags + * + * Creates a new file by hooking it on a single inode. This is + * useful for files that do not need to have a full-fledged inode in + * order to operate correctly. All the files created with + * anon_inode_getfd() will use the same singleton inode, reducing + * memory use and avoiding code duplication for the file/inode/dentry + * setup. Returns a newly created file descriptor or an error code. + */ +int anon_inode_getfd(const char *name, const struct file_operations *fops, + void *priv, int flags) +{ + return _anon_inode_getfd(name, fops, priv, flags, NULL, false); +} EXPORT_SYMBOL_GPL(anon_inode_getfd); +/** + * Like anon_inode_getfd(), but adds the @context_inode argument to + * allow security modules to control creation of the new file. Once the + * security module makes the decision, this inode is no longer needed + * and hence reference to it is not held. + */ +int anon_inode_getfd_secure(const char *name, const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode) +{ + return _anon_inode_getfd(name, fops, priv, flags, context_inode, true); +} +EXPORT_SYMBOL_GPL(anon_inode_getfd_secure); + static int __init anon_inode_init(void) { anon_inode_mnt = kern_mount(&anon_inode_fs_type); diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h index d0d7d96261ad..6ab840ee93bc 100644 --- a/include/linux/anon_inodes.h +++ b/include/linux/anon_inodes.h @@ -10,12 +10,20 @@ #define _LINUX_ANON_INODES_H struct file_operations; +struct inode; struct file *anon_inode_getfile(const char *name, const struct file_operations *fops, void *priv, int flags); + +int anon_inode_getfd_secure(const char *name, + const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode); + int anon_inode_getfd(const char *name, const struct file_operations *fops, void *priv, int flags); + #endif /* _LINUX_ANON_INODES_H */ diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 2a8c74d99015..35ff75c43de4 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -113,6 +113,8 @@ LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode) LSM_HOOK(int, 0, inode_init_security, struct inode *inode, struct inode *dir, const struct qstr *qstr, const char **name, void **value, size_t *len) +LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode, + const struct qstr *name, const struct inode *context_inode) LSM_HOOK(int, 0, inode_create, struct inode *dir, struct dentry *dentry, umode_t mode) LSM_HOOK(int, 0, inode_link, struct dentry *old_dentry, struct inode *dir, diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 9e2e3e63719d..586186f1184b 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -233,6 +233,15 @@ * 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 the incore security field for the new anonymous inode + * and return whether the inode creation is permitted by the security + * module or not. + * @inode contains the inode structure + * @name name of the anonymous inode class + * @context_inode optional related inode + * Returns 0 on success, -EACCESS if the security module denies the + * creation of this inode, or another -errno upon other errors. * @inode_create: * Check permission to create a regular file. * @dir contains inode structure of the parent of the new file. diff --git a/include/linux/security.h b/include/linux/security.h index 0a0a03b36a3b..7c6b3dcf4721 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -322,6 +322,9 @@ 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 struct qstr *name, + const struct inode *context_inode); int security_old_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, const char **name, void **value, size_t *len); @@ -732,6 +735,13 @@ static inline int security_inode_init_security(struct inode *inode, return 0; } +static inline int security_inode_init_security_anon(struct inode *inode, + const struct qstr *name, + const struct inode *context_inode) +{ + return 0; +} + static inline int security_old_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, diff --git a/security/security.c b/security/security.c index 70a7ad357bc6..2c4b121a01b9 100644 --- a/security/security.c +++ b/security/security.c @@ -1057,6 +1057,14 @@ 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 struct qstr *name, + const struct inode *context_inode) +{ + return call_int_hook(inode_init_security_anon, 0, inode, name, + context_inode); +} + int security_old_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, const char **name, void **value, size_t *len)