[PATCH v2 1/2] LSM: SafeSetID: gate setgid transitions
mortonm at chromium.org
mortonm at chromium.org
Wed Feb 27 20:00:03 UTC 2019
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>
---
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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