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Message-Id: <20180731232351.122951-1-mortonm@chromium.org>
Date: Tue, 31 Jul 2018 16:23:51 -0700
From: Micah Morton <mortonm@...omium.org>
To: rdunlap@...radead.org
Cc: jmorris@...ei.org, linux-security-module@...r.kernel.org,
serge@...lyn.com, keescook@...omium.org,
linux-kernel@...r.kernel.org, Micah Morton <mortonm@...omium.org>
Subject: [PATCH] security: Add LSM fixup hooks to set*gid syscalls.
The set*uid system calls all call an LSM fixup hook called
security_task_fix_setuid, which allows for altering the behavior of those
calls by a security module. Comments explaining the LSM_SETID_* constants
in /include/linux/security.h imply that the constants are to be used for
both the set*uid and set*gid syscalls, but the set*gid syscalls do not
have the relevant hooks, meaning a security module can only alter syscalls
that change user identity attributes but not ones that change group
identity attributes. This patch adds the necessary LSM hook, called
security_task_fix_setgid, and calls the hook from the appropriate places
in the set*gid syscalls.Tested by putting a print statement in the hook and
seeing it triggered from the various set*gid syscalls.
Signed-off-by: Micah Morton <mortonm@...omium.org>
Acked-by: Kees Cook <keescook@...omium.org>
---
NOTE: the security_task_fix_setgid line in sys_setfsgid is over 80
characters, but I figured I'd just follow how it was done in sys_setfsuid
rather than trying to wrap the line, since the functions are nearly
identical.
---
include/linux/lsm_hooks.h | 12 ++++++++++++
include/linux/security.h | 9 +++++++++
kernel/sys.c | 15 ++++++++++++++-
security/security.c | 6 ++++++
4 files changed, 41 insertions(+), 1 deletion(-)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 8f1131c8dd54..a2166c812a97 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -599,6 +599,15 @@
* @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.
@@ -1587,6 +1596,8 @@ 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);
@@ -1876,6 +1887,7 @@ 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 63030c85ee19..a82d97cf13ab 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -325,6 +325,8 @@ 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);
@@ -929,6 +931,13 @@ 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 38509dc1f77b..f6ef922c6815 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -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:
@@ -434,6 +438,10 @@ long __sys_setgid(gid_t gid)
else
goto error;
+ retval = security_task_fix_setgid(new, old, LSM_SETID_ID);
+ if (retval < 0)
+ goto error;
+
return commit_creds(new);
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:
@@ -861,7 +873,8 @@ long __sys_setfsgid(gid_t gid)
ns_capable(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 68f46d849abe..587786fc0aaa 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1062,6 +1062,12 @@ 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);
--
2.18.0.345.g5c9ce644c3-goog
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