Re: [PATCH 1/3] security: Add LSM hook to setgroups() syscall
flat view
From: Casey Schaufler <casey@schaufler-ca.com>
Date: 2022-06-20 18:15:29
Also in:
lkml
On 6/16/2022 10:18 AM, Micah Morton wrote:
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. Signed-off-by: Micah Morton <mortonm@chromium.org>
I don't see any problems with this. Acked-by: Casey Schaufler <casey@schaufler-ca.com>
quoted hunk ↗ jump to hunk
--- include/linux/lsm_hook_defs.h | 1 + include/linux/lsm_hooks.h | 7 +++++++ include/linux/security.h | 7 +++++++ kernel/groups.c | 13 +++++++++++++ security/security.c | 5 +++++ 5 files changed, 33 insertions(+)diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index eafa1d2489fd..806448173033 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h@@ -201,6 +201,7 @@ LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old, int flags) LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old, int flags) +LSM_HOOK(int, 0, task_fix_setgroups, struct cred *new, const struct cred * old) LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid) LSM_HOOK(int, 0, task_getpgid, struct task_struct *p) LSM_HOOK(int, 0, task_getsid, struct task_struct *p)diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 91c8146649f5..84a0d7e02176 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h@@ -702,6 +702,13 @@ * @old is the set of credentials that are being replaced. * @flags contains one of the LSM_SETID_* values. * Return 0 on success. + * @task_fix_setgroups: + * Update the module's state after setting the supplementary group + * identity attributes of the current process. + * @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. + * Return 0 on success. * @task_setpgid: * Check permission before setting the process group identifier of the * process @p to @pgid.diff --git a/include/linux/security.h b/include/linux/security.h index 7fc4e9f49f54..1dfd32c49fa3 100644 --- a/include/linux/security.h +++ b/include/linux/security.h@@ -415,6 +415,7 @@ 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_fix_setgroups(struct cred *new, const struct cred *old); 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);@@ -1098,6 +1099,12 @@ static inline int security_task_fix_setgid(struct cred *new, return 0; } +static inline int security_task_fix_setgroups(struct cred *new, + const struct cred *old) +{ + return 0; +} + static inline int security_task_setpgid(struct task_struct *p, pid_t pgid) { return 0;diff --git a/kernel/groups.c b/kernel/groups.c index 787b381c7c00..9aaed2a31073 100644 --- a/kernel/groups.c +++ b/kernel/groups.c@@ -134,13 +134,26 @@ EXPORT_SYMBOL(set_groups); int set_current_groups(struct group_info *group_info) { struct cred *new; + const struct cred *old; + int retval; new = prepare_creds(); if (!new) return -ENOMEM; + old = current_cred(); + set_groups(new, group_info); + + retval = security_task_fix_setgroups(new, old); + if (retval < 0) + goto error; + return commit_creds(new); + +error: + abort_creds(new); + return retval; } EXPORT_SYMBOL(set_current_groups);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);