From fcfe0ac2fcfae7d5fcad3d0375cb8ff38caf8aba Mon Sep 17 00:00:00 2001 From: Micah Morton Date: Wed, 8 Jun 2022 20:57:11 +0000 Subject: security: Add LSM hook to setgroups() syscall Give the LSM framework the ability to filter setgroups() syscalls. There are already analagous hooks for the set*uid() and set*gid() syscalls. The SafeSetID LSM will use this new hook to ensure setgroups() calls are allowed by the installed security policy. Tested by putting print statement in security_task_fix_setgroups() hook and confirming that it gets hit when userspace does a setgroups() syscall. Acked-by: Casey Schaufler Reviewed-by: Serge Hallyn Signed-off-by: Micah Morton --- security/security.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'security') diff --git a/security/security.c b/security/security.c index 188b8f782220..15c686145ad6 100644 --- a/security/security.c +++ b/security/security.c @@ -1803,6 +1803,11 @@ int security_task_fix_setgid(struct cred *new, const struct cred *old, return call_int_hook(task_fix_setgid, 0, new, old, flags); } +int security_task_fix_setgroups(struct cred *new, const struct cred *old) +{ + return call_int_hook(task_fix_setgroups, 0, new, old); +} + int security_task_setpgid(struct task_struct *p, pid_t pgid) { return call_int_hook(task_setpgid, 0, p, pgid); -- cgit v1.2.3 From 3e3374d382ff250502fbc4407001ac793d5c4e7f Mon Sep 17 00:00:00 2001 From: Micah Morton Date: Wed, 8 Jun 2022 22:27:27 +0000 Subject: LSM: SafeSetID: Add setgroups() security policy handling The SafeSetID LSM has functionality for restricting setuid()/setgid() syscalls based on its configured security policies. This patch adds the analogous functionality for the setgroups() syscall. Security policy for the setgroups() syscall follows the same policies that are installed on the system for setgid() syscalls. Signed-off-by: Micah Morton --- security/safesetid/lsm.c | 39 ++++++++++++++++++++++++++++++--------- 1 file changed, 30 insertions(+), 9 deletions(-) (limited to 'security') diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c index 963f4ad9cb66..e806739f7868 100644 --- a/security/safesetid/lsm.c +++ b/security/safesetid/lsm.c @@ -97,15 +97,9 @@ static int safesetid_security_capable(const struct cred *cred, return 0; /* - * If CAP_SET{U/G}ID is currently used for a setid() syscall, we want to - * let it go through here; the real security check happens later, in the - * task_fix_set{u/g}id hook. - * - * NOTE: - * Until we add support for restricting setgroups() calls, GID security - * policies offer no meaningful security since we always return 0 here - * when called from within the setgroups() syscall and there is no - * additional hook later on to enforce security policies for setgroups(). + * If CAP_SET{U/G}ID is currently used for a setid or setgroups syscall, we + * want to let it go through here; the real security check happens later, in + * the task_fix_set{u/g}id or task_fix_setgroups hooks. */ if ((opts & CAP_OPT_INSETID) != 0) return 0; @@ -241,9 +235,36 @@ static int safesetid_task_fix_setgid(struct cred *new, return -EACCES; } +static int safesetid_task_fix_setgroups(struct cred *new, const struct cred *old) +{ + int i; + + /* Do nothing if there are no setgid restrictions for our old RGID. */ + if (setid_policy_lookup((kid_t){.gid = old->gid}, INVALID_ID, GID) == SIDPOL_DEFAULT) + return 0; + + get_group_info(new->group_info); + for (i = 0; i < new->group_info->ngroups; i++) { + if (!id_permitted_for_cred(old, (kid_t){.gid = new->group_info->gid[i]}, GID)) { + put_group_info(new->group_info); + /* + * Kill this process to avoid potential security vulnerabilities + * that could arise from a missing allowlist entry preventing a + * privileged process from dropping to a lesser-privileged one. + */ + force_sig(SIGKILL); + return -EACCES; + } + } + + put_group_info(new->group_info); + return 0; +} + static struct security_hook_list safesetid_security_hooks[] = { LSM_HOOK_INIT(task_fix_setuid, safesetid_task_fix_setuid), LSM_HOOK_INIT(task_fix_setgid, safesetid_task_fix_setgid), + LSM_HOOK_INIT(task_fix_setgroups, safesetid_task_fix_setgroups), LSM_HOOK_INIT(capable, safesetid_security_capable) }; -- cgit v1.2.3