[PATCH v2 1/2] LSM: SafeSetID: gate setgid transitions
Serge E. Hallyn
serge at hallyn.com
Thu Feb 28 03:11:22 UTC 2019
On Wed, Feb 27, 2019 at 12:00:03PM -0800, mortonm at chromium.org wrote:
> From: Micah Morton <mortonm at chromium.org>
>
> This patch adds a 'task_fix_setgid' LSM hook, which is analogous to the
> existing 'task_fix_setuid' LSM hook, and calls this new hook from the
> setgid functions in kernel/sys.c. This will allow the SafeSetID LSM to
> govern setgid transitions in addition to setuid transitions. This change
> also makes sure the setgid functions in kernel/sys.c call
> security_capable_setid rather than the ordinary security_capable
> function, so that the security_capable hook in the SafeSetID LSM knows
> it is being invoked from a setid function.
>
> Signed-off-by: Micah Morton <mortonm at chromium.org>
Acked-by: Serge Hallyn <serge at hallyn.com>
> ---
> Changes since the last patch: took out the cap_task_fix_setgid stuff
> from include/linux/security.h since this hook won't be hooked by
> security/commoncap.c.
> include/linux/lsm_hooks.h | 12 ++++++++++++
> include/linux/security.h | 9 +++++++++
> kernel/sys.c | 27 +++++++++++++++++++++------
> security/security.c | 6 ++++++
> 4 files changed, 48 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 22fc786d723a..f252ed3e95ef 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -603,6 +603,15 @@
> * @old is the set of credentials that are being replaces
> * @flags contains one of the LSM_SETID_* values.
> * Return 0 on success.
> + * @task_fix_setgid:
> + * Update the module's state after setting one or more of the group
> + * identity attributes of the current process. The @flags parameter
> + * indicates which of the set*gid system calls invoked this hook.
> + * @new is the set of credentials that will be installed. Modifications
> + * should be made to this rather than to @current->cred.
> + * @old is the set of credentials that are being replaced
> + * @flags contains one of the LSM_SETID_* values.
> + * Return 0 on success.
> * @task_setpgid:
> * Check permission before setting the process group identifier of the
> * process @p to @pgid.
> @@ -1596,6 +1605,8 @@ union security_list_options {
> enum kernel_read_file_id id);
> int (*task_fix_setuid)(struct cred *new, const struct cred *old,
> int flags);
> + int (*task_fix_setgid)(struct cred *new, const struct cred *old,
> + int flags);
> int (*task_setpgid)(struct task_struct *p, pid_t pgid);
> int (*task_getpgid)(struct task_struct *p);
> int (*task_getsid)(struct task_struct *p);
> @@ -1887,6 +1898,7 @@ struct security_hook_heads {
> struct hlist_head kernel_post_read_file;
> struct hlist_head kernel_module_request;
> struct hlist_head task_fix_setuid;
> + struct hlist_head task_fix_setgid;
> struct hlist_head task_setpgid;
> struct hlist_head task_getpgid;
> struct hlist_head task_getsid;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 13537a49ae97..e28ef6bf6280 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -326,6 +326,8 @@ int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
> enum kernel_read_file_id id);
> int security_task_fix_setuid(struct cred *new, const struct cred *old,
> int flags);
> +int security_task_fix_setgid(struct cred *new, const struct cred *old,
> + int flags);
> int security_task_setpgid(struct task_struct *p, pid_t pgid);
> int security_task_getpgid(struct task_struct *p);
> int security_task_getsid(struct task_struct *p);
> @@ -930,6 +932,13 @@ static inline int security_task_fix_setuid(struct cred *new,
> return cap_task_fix_setuid(new, old, flags);
> }
>
> +static inline int security_task_fix_setgid(struct cred *new,
> + const struct cred *old,
> + int flags)
> +{
> + return 0;
> +}
> +
> static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
> {
> return 0;
> diff --git a/kernel/sys.c b/kernel/sys.c
> index c5f875048aef..76f1c46ac66f 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -372,7 +372,7 @@ long __sys_setregid(gid_t rgid, gid_t egid)
> if (rgid != (gid_t) -1) {
> if (gid_eq(old->gid, krgid) ||
> gid_eq(old->egid, krgid) ||
> - ns_capable(old->user_ns, CAP_SETGID))
> + ns_capable_setid(old->user_ns, CAP_SETGID))
> new->gid = krgid;
> else
> goto error;
> @@ -381,7 +381,7 @@ long __sys_setregid(gid_t rgid, gid_t egid)
> if (gid_eq(old->gid, kegid) ||
> gid_eq(old->egid, kegid) ||
> gid_eq(old->sgid, kegid) ||
> - ns_capable(old->user_ns, CAP_SETGID))
> + ns_capable_setid(old->user_ns, CAP_SETGID))
> new->egid = kegid;
> else
> goto error;
> @@ -392,6 +392,10 @@ long __sys_setregid(gid_t rgid, gid_t egid)
> new->sgid = new->egid;
> new->fsgid = new->egid;
>
> + retval = security_task_fix_setgid(new, old, LSM_SETID_RE);
> + if (retval < 0)
> + goto error;
> +
> return commit_creds(new);
>
> error:
> @@ -427,13 +431,17 @@ long __sys_setgid(gid_t gid)
> old = current_cred();
>
> retval = -EPERM;
> - if (ns_capable(old->user_ns, CAP_SETGID))
> + if (ns_capable_setid(old->user_ns, CAP_SETGID))
> new->gid = new->egid = new->sgid = new->fsgid = kgid;
> else if (gid_eq(kgid, old->gid) || gid_eq(kgid, old->sgid))
> new->egid = new->fsgid = kgid;
> else
> goto error;
>
> + retval = security_task_fix_setgid(new, old, LSM_SETID_ID);
> + if (retval < 0)
> + goto error;
> +
> return commit_creds(new);
>
> error:
> @@ -735,7 +743,7 @@ long __sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
> old = current_cred();
>
> retval = -EPERM;
> - if (!ns_capable(old->user_ns, CAP_SETGID)) {
> + if (!ns_capable_setid(old->user_ns, CAP_SETGID)) {
> if (rgid != (gid_t) -1 && !gid_eq(krgid, old->gid) &&
> !gid_eq(krgid, old->egid) && !gid_eq(krgid, old->sgid))
> goto error;
> @@ -755,6 +763,10 @@ long __sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
> new->sgid = ksgid;
> new->fsgid = new->egid;
>
> + retval = security_task_fix_setgid(new, old, LSM_SETID_RES);
> + if (retval < 0)
> + goto error;
> +
> return commit_creds(new);
>
> error:
> @@ -858,10 +870,13 @@ long __sys_setfsgid(gid_t gid)
>
> if (gid_eq(kgid, old->gid) || gid_eq(kgid, old->egid) ||
> gid_eq(kgid, old->sgid) || gid_eq(kgid, old->fsgid) ||
> - ns_capable(old->user_ns, CAP_SETGID)) {
> + ns_capable_setid(old->user_ns, CAP_SETGID)) {
> if (!gid_eq(kgid, old->fsgid)) {
> new->fsgid = kgid;
> - goto change_okay;
> + if (security_task_fix_setgid(new,
> + old,
> + LSM_SETID_FS) == 0)
> + goto change_okay;
> }
> }
>
> diff --git a/security/security.c b/security/security.c
> index ed9b8cbf21cf..7e936f944a66 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1574,6 +1574,12 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
> return call_int_hook(task_fix_setuid, 0, new, old, flags);
> }
>
> +int security_task_fix_setgid(struct cred *new, const struct cred *old,
> + int flags)
> +{
> + return call_int_hook(task_fix_setgid, 0, new, old, flags);
> +}
> +
> int security_task_setpgid(struct task_struct *p, pid_t pgid)
> {
> return call_int_hook(task_setpgid, 0, p, pgid);
> --
> 2.21.0.352.gf09ad66450-goog
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