Messages in this thread | | | Date | Wed, 3 Aug 2022 08:13:15 -0500 | Subject | Re: [PATCH v4 1/4] security, lsm: Introduce security_create_user_ns() | From | Frederick Lawler <> |
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On 8/2/22 4:47 PM, KP Singh wrote: > On Mon, Aug 1, 2022 at 8:02 PM Frederick Lawler <fred@cloudflare.com> wrote: >> >> Preventing user namespace (privileged or otherwise) creation comes in a >> few of forms in order of granularity: >> >> 1. /proc/sys/user/max_user_namespaces sysctl >> 2. OS specific patch(es) >> 3. CONFIG_USER_NS >> >> To block a task based on its attributes, the LSM hook cred_prepare is a >> good candidate for use because it provides more granular control, and >> it is called before create_user_ns(): >> >> cred = prepare_creds() >> security_prepare_creds() >> call_int_hook(cred_prepare, ... >> if (cred) >> create_user_ns(cred) >> >> Since security_prepare_creds() is meant for LSMs to copy and prepare >> credentials, access control is an unintended use of the hook. Therefore >> introduce a new function security_create_user_ns() with an accompanying >> userns_create LSM hook. >> >> This hook takes the prepared creds for LSM authors to write policy >> against. On success, the new namespace is applied to credentials, >> otherwise an error is returned. >> >> Signed-off-by: Frederick Lawler <fred@cloudflare.com> >> Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org> > > Reviewed-by: KP Singh <kpsingh@kernel.org> > > This looks useful, and I would also like folks to consider the > observability aspects of BPF LSM as > brought up here: > > https://lore.kernel.org/all/CAEiveUdPhEPAk7Y0ZXjPsD=Vb5hn453CHzS9aG-tkyRa8bf_eg@mail.gmail.com/ > > Frederick, what about adding the observability aspects to the commit > description as well.
Agreed. I'll include that in v5.
> > - KP > >> >> --- >> Changes since v3: >> - No changes >> Changes since v2: >> - Rename create_user_ns hook to userns_create >> Changes since v1: >> - Changed commit wording >> - Moved execution to be after id mapping check >> - Changed signature to only accept a const struct cred * >> --- >> include/linux/lsm_hook_defs.h | 1 + >> include/linux/lsm_hooks.h | 4 ++++ >> include/linux/security.h | 6 ++++++ >> kernel/user_namespace.c | 5 +++++ >> security/security.c | 5 +++++ >> 5 files changed, 21 insertions(+) >> >> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h >> index eafa1d2489fd..7ff93cb8ca8d 100644 >> --- a/include/linux/lsm_hook_defs.h >> +++ b/include/linux/lsm_hook_defs.h >> @@ -223,6 +223,7 @@ LSM_HOOK(int, -ENOSYS, task_prctl, int option, unsigned long arg2, >> unsigned long arg3, unsigned long arg4, unsigned long arg5) >> LSM_HOOK(void, LSM_RET_VOID, task_to_inode, struct task_struct *p, >> struct inode *inode) >> +LSM_HOOK(int, 0, userns_create, const struct cred *cred) >> LSM_HOOK(int, 0, ipc_permission, struct kern_ipc_perm *ipcp, short flag) >> LSM_HOOK(void, LSM_RET_VOID, ipc_getsecid, struct kern_ipc_perm *ipcp, >> u32 *secid) >> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h >> index 91c8146649f5..54fe534d0e01 100644 >> --- a/include/linux/lsm_hooks.h >> +++ b/include/linux/lsm_hooks.h >> @@ -799,6 +799,10 @@ >> * security attributes, e.g. for /proc/pid inodes. >> * @p contains the task_struct for the task. >> * @inode contains the inode structure for the inode. >> + * @userns_create: >> + * Check permission prior to creating a new user namespace. >> + * @cred points to prepared creds. >> + * Return 0 if successful, otherwise < 0 error code. >> * >> * Security hooks for Netlink messaging. >> * >> diff --git a/include/linux/security.h b/include/linux/security.h >> index 7fc4e9f49f54..a195bf33246a 100644 >> --- a/include/linux/security.h >> +++ b/include/linux/security.h >> @@ -435,6 +435,7 @@ int security_task_kill(struct task_struct *p, struct kernel_siginfo *info, >> int security_task_prctl(int option, unsigned long arg2, unsigned long arg3, >> unsigned long arg4, unsigned long arg5); >> void security_task_to_inode(struct task_struct *p, struct inode *inode); >> +int security_create_user_ns(const struct cred *cred); >> int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag); >> void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid); >> int security_msg_msg_alloc(struct msg_msg *msg); >> @@ -1185,6 +1186,11 @@ static inline int security_task_prctl(int option, unsigned long arg2, >> static inline void security_task_to_inode(struct task_struct *p, struct inode *inode) >> { } >> >> +static inline int security_create_user_ns(const struct cred *cred) >> +{ >> + return 0; >> +} >> + >> static inline int security_ipc_permission(struct kern_ipc_perm *ipcp, >> short flag) >> { >> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c >> index 5481ba44a8d6..3f464bbda0e9 100644 >> --- a/kernel/user_namespace.c >> +++ b/kernel/user_namespace.c >> @@ -9,6 +9,7 @@ >> #include <linux/highuid.h> >> #include <linux/cred.h> >> #include <linux/securebits.h> >> +#include <linux/security.h> >> #include <linux/keyctl.h> >> #include <linux/key-type.h> >> #include <keys/user-type.h> >> @@ -113,6 +114,10 @@ int create_user_ns(struct cred *new) >> !kgid_has_mapping(parent_ns, group)) >> goto fail_dec; >> >> + ret = security_create_user_ns(new); >> + if (ret < 0) >> + goto fail_dec; >> + >> ret = -ENOMEM; >> ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL); >> if (!ns) >> diff --git a/security/security.c b/security/security.c >> index 188b8f782220..ec9b4696e86c 100644 >> --- a/security/security.c >> +++ b/security/security.c >> @@ -1903,6 +1903,11 @@ void security_task_to_inode(struct task_struct *p, struct inode *inode) >> call_void_hook(task_to_inode, p, inode); >> } >> >> +int security_create_user_ns(const struct cred *cred) >> +{ >> + return call_int_hook(userns_create, 0, cred); >> +} >> + >> int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) >> { >> return call_int_hook(ipc_permission, 0, ipcp, flag); >> -- >> 2.30.2 >>
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