| Message ID | 20200923193324.3090160-1-lokeshgidra@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | SELinux support for anonymous inodes and UFFD | expand |
On Wed, Sep 23, 2020 at 12:33 PM Lokesh Gidra <lokeshgidra@google.com> wrote: > > Userfaultfd in unprivileged contexts could be potentially very > useful. We'd like to harden userfaultfd to make such unprivileged use > less risky. This patch series allows SELinux to manage userfaultfd > file descriptors and in the future, other kinds of > anonymous-inode-based file descriptor. SELinux policy authors can > apply policy types to anonymous inodes by providing name-based > transition rules keyed off the anonymous inode internal name ( > "[userfaultfd]" in the case of userfaultfd(2) file descriptors) and > applying policy to the new SIDs thus produced. > > With SELinux managed userfaultfd, an admin can control creation and > movement of the file descriptors. In particular, handling of > a userfaultfd descriptor by a different process is essentially a > ptrace access into the process, without any of the corresponding > security_ptrace_access_check() checks. For privacy, the admin may > want to deny such accesses, which is possible with SELinux support. > > Inside the kernel, a new anon_inode interface, anon_inode_getfd_secure, > allows callers to opt into this SELinux management. In this new "secure" > mode, anon_inodes create new ephemeral inodes for anonymous file objects > instead of reusing the normal anon_inodes singleton dummy inode. A new > LSM hook gives security modules an opportunity to configure and veto > these ephemeral inodes. > > This patch series is one of two fork of [1] and is an > alternative to [2]. > > The primary difference between the two patch series is that this > partch series creates a unique inode for each "secure" anonymous > inode, while the other patch series ([2]) continues using the > singleton dummy anonymous inode and adds a way to attach SELinux > security information directly to file objects. > > I prefer the approach in this patch series because 1) it's a smaller > patch than [2], and 2) it produces a more regular security > architecture: in this patch series, secure anonymous inodes aren't > S_PRIVATE and they maintain the SELinux property that the label for a > file is in its inode. We do need an additional inode per anonymous > file, but per-struct-file inode creation doesn't seem to be a problem > for pipes and sockets. > > The previous version of this feature ([1]) created a new SELinux > security class for userfaultfd file descriptors. This version adopts > the generic transition-based approach of [2]. > > This patch series also differs from [2] in that it doesn't affect all > anonymous inodes right away --- instead requiring anon_inodes callers > to opt in --- but this difference isn't one of basic approach. The > important question to resolve is whether we should be creating new > inodes or enhancing per-file data. > > Changes from the first version of the patch: > > - Removed some error checks > - Defined a new anon_inode SELinux class to resolve the > ambiguity in [3] > - Inherit sclass as well as descriptor from context inode > > Changes from the second version of the patch: > > - Fixed example policy in the commit message to reflect the use of > the new anon_inode class. > > Changes from the third version of the patch: > > - Dropped the fops parameter to the LSM hook > - Documented hook parameters > - Fixed incorrect class used for SELinux transition > - Removed stray UFFD changed early in the series > - Removed a redundant ERR_PTR(PTR_ERR()) > > Changes from the fourth version of the patch: > > - Removed an unused parameter from an internal function > - Fixed function documentation > > Changes from the fifth version of the patch: > > - Fixed function documentation in fs/anon_inodes.c and > include/linux/lsm_hooks.h > - Used anon_inode_getfd_secure() in userfaultfd() syscall and removed > owner from userfaultfd_ctx. > > Changes from the sixth version of the patch: > > - Removed definition of anon_inode_getfile_secure() as there are no > callers. > - Simplified function description of anon_inode_getfd_secure(). > - Elaborated more on the purpose of 'context_inode' in commit message. > > Changes from the seventh version of the patch: > > - Fixed error handling in _anon_inode_getfile(). > - Fixed minor comment and indentation related issues. > > Changes from the eighth version of the patch: > > - Replaced selinux_state.initialized with selinux_state.initialized > Is there anything else that needs to be done before merging this patch series? I urge the reviewers to please take a look. > > [1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@google.com/ > [2] https://lore.kernel.org/linux-fsdevel/20200213194157.5877-1-sds@tycho.nsa.gov/ > [3] https://lore.kernel.org/lkml/23f725ca-5b5a-5938-fcc8-5bbbfc9ba9bc@tycho.nsa.gov/ > > Daniel Colascione (3): > Add a new LSM-supporting anonymous inode interface > Teach SELinux about anonymous inodes > Wire UFFD up to SELinux > > fs/anon_inodes.c | 147 ++++++++++++++++++++-------- > fs/userfaultfd.c | 19 ++-- > 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 ++ > security/selinux/hooks.c | 53 ++++++++++ > security/selinux/include/classmap.h | 2 + > 9 files changed, 209 insertions(+), 49 deletions(-) > > -- > 2.28.0.681.g6f77f65b4e-goog >
On Wed, 7 Oct 2020, Lokesh Gidra wrote: > Is there anything else that needs to be done before merging this > patch series? I urge the reviewers to please take a look. > It looks generally fine to me from a security POV, we really need some feedback from VFS folk.
Userfaultfd in unprivileged contexts could be potentially very useful. We'd like to harden userfaultfd to make such unprivileged use less risky. This patch series allows SELinux to manage userfaultfd file descriptors and in the future, other kinds of anonymous-inode-based file descriptor. SELinux policy authors can apply policy types to anonymous inodes by providing name-based transition rules keyed off the anonymous inode internal name ( "[userfaultfd]" in the case of userfaultfd(2) file descriptors) and applying policy to the new SIDs thus produced. With SELinux managed userfaultfd, an admin can control creation and movement of the file descriptors. In particular, handling of a userfaultfd descriptor by a different process is essentially a ptrace access into the process, without any of the corresponding security_ptrace_access_check() checks. For privacy, the admin may want to deny such accesses, which is possible with SELinux support. Inside the kernel, a new anon_inode interface, anon_inode_getfd_secure, allows callers to opt into this SELinux management. In this new "secure" mode, anon_inodes create new ephemeral inodes for anonymous file objects instead of reusing the normal anon_inodes singleton dummy inode. A new LSM hook gives security modules an opportunity to configure and veto these ephemeral inodes. This patch series is one of two fork of [1] and is an alternative to [2]. The primary difference between the two patch series is that this partch series creates a unique inode for each "secure" anonymous inode, while the other patch series ([2]) continues using the singleton dummy anonymous inode and adds a way to attach SELinux security information directly to file objects. I prefer the approach in this patch series because 1) it's a smaller patch than [2], and 2) it produces a more regular security architecture: in this patch series, secure anonymous inodes aren't S_PRIVATE and they maintain the SELinux property that the label for a file is in its inode. We do need an additional inode per anonymous file, but per-struct-file inode creation doesn't seem to be a problem for pipes and sockets. The previous version of this feature ([1]) created a new SELinux security class for userfaultfd file descriptors. This version adopts the generic transition-based approach of [2]. This patch series also differs from [2] in that it doesn't affect all anonymous inodes right away --- instead requiring anon_inodes callers to opt in --- but this difference isn't one of basic approach. The important question to resolve is whether we should be creating new inodes or enhancing per-file data. Changes from the first version of the patch: - Removed some error checks - Defined a new anon_inode SELinux class to resolve the ambiguity in [3] - Inherit sclass as well as descriptor from context inode Changes from the second version of the patch: - Fixed example policy in the commit message to reflect the use of the new anon_inode class. Changes from the third version of the patch: - Dropped the fops parameter to the LSM hook - Documented hook parameters - Fixed incorrect class used for SELinux transition - Removed stray UFFD changed early in the series - Removed a redundant ERR_PTR(PTR_ERR()) Changes from the fourth version of the patch: - Removed an unused parameter from an internal function - Fixed function documentation Changes from the fifth version of the patch: - Fixed function documentation in fs/anon_inodes.c and include/linux/lsm_hooks.h - Used anon_inode_getfd_secure() in userfaultfd() syscall and removed owner from userfaultfd_ctx. Changes from the sixth version of the patch: - Removed definition of anon_inode_getfile_secure() as there are no callers. - Simplified function description of anon_inode_getfd_secure(). - Elaborated more on the purpose of 'context_inode' in commit message. Changes from the seventh version of the patch: - Fixed error handling in _anon_inode_getfile(). - Fixed minor comment and indentation related issues. Changes from the eighth version of the patch: - Replaced selinux_state.initialized with selinux_state.initialized [1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@google.com/ [2] https://lore.kernel.org/linux-fsdevel/20200213194157.5877-1-sds@tycho.nsa.gov/ [3] https://lore.kernel.org/lkml/23f725ca-5b5a-5938-fcc8-5bbbfc9ba9bc@tycho.nsa.gov/ Daniel Colascione (3): Add a new LSM-supporting anonymous inode interface Teach SELinux about anonymous inodes Wire UFFD up to SELinux fs/anon_inodes.c | 147 ++++++++++++++++++++-------- fs/userfaultfd.c | 19 ++-- 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 ++ security/selinux/hooks.c | 53 ++++++++++ security/selinux/include/classmap.h | 2 + 9 files changed, 209 insertions(+), 49 deletions(-)