[PATCH 4.14 2/2] binder: use cred instead of task for selinux checks
Todd Kjos
tkjos at google.com
Wed Nov 10 23:00:03 UTC 2021
commit 52f88693378a58094c538662ba652aff0253c4fe upstream.
Since binder was integrated with selinux, it has passed
'struct task_struct' associated with the binder_proc
to represent the source and target of transactions.
The conversion of task to SID was then done in the hook
implementations. It turns out that there are race conditions
which can result in an incorrect security context being used.
Fix by using the 'struct cred' saved during binder_open and pass
it to the selinux subsystem.
Cc: stable at vger.kernel.org # 5.14 (need backport for earlier stables)
Fixes: 79af73079d75 ("Add security hooks to binder and implement the hooks for SELinux.")
Suggested-by: Jann Horn <jannh at google.com>
Signed-off-by: Todd Kjos <tkjos at google.com>
Acked-by: Casey Schaufler <casey at schaufler-ca.com>
Signed-off-by: Paul Moore <paul at paul-moore.com>
Change-Id: Id7157515d2b08f11683aeb8ad9b8f1da075d34e7
---
drivers/android/binder.c | 12 ++++++------
include/linux/lsm_hooks.h | 28 ++++++++++++++--------------
include/linux/security.h | 28 ++++++++++++++--------------
security/security.c | 14 +++++++-------
security/selinux/hooks.c | 31 +++++++++++++------------------
5 files changed, 54 insertions(+), 59 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 332b4a2cbb94..c5fd7908fc91 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2285,7 +2285,7 @@ static int binder_translate_binder(struct flat_binder_object *fp,
ret = -EINVAL;
goto done;
}
- if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+ if (security_binder_transfer_binder(proc->cred, target_proc->cred)) {
ret = -EPERM;
goto done;
}
@@ -2331,7 +2331,7 @@ static int binder_translate_handle(struct flat_binder_object *fp,
proc->pid, thread->pid, fp->handle);
return -EINVAL;
}
- if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) {
+ if (security_binder_transfer_binder(proc->cred, target_proc->cred)) {
ret = -EPERM;
goto done;
}
@@ -2415,7 +2415,7 @@ static int binder_translate_fd(int fd,
ret = -EBADF;
goto err_fget;
}
- ret = security_binder_transfer_file(proc->tsk, target_proc->tsk, file);
+ ret = security_binder_transfer_file(proc->cred, target_proc->cred, file);
if (ret < 0) {
ret = -EPERM;
goto err_security;
@@ -2802,8 +2802,8 @@ static void binder_transaction(struct binder_proc *proc,
return_error_line = __LINE__;
goto err_invalid_target_handle;
}
- if (security_binder_transaction(proc->tsk,
- target_proc->tsk) < 0) {
+ if (security_binder_transaction(proc->cred,
+ target_proc->cred) < 0) {
return_error = BR_FAILED_REPLY;
return_error_param = -EPERM;
return_error_line = __LINE__;
@@ -4469,7 +4469,7 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
ret = -EBUSY;
goto out;
}
- ret = security_binder_set_context_mgr(proc->tsk);
+ ret = security_binder_set_context_mgr(proc->cred);
if (ret < 0)
goto out;
if (uid_valid(context->binder_context_mgr_uid)) {
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index c9258124e417..569debc49f3d 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1170,22 +1170,22 @@
*
* @binder_set_context_mgr:
* Check whether @mgr is allowed to be the binder context manager.
- * @mgr contains the task_struct for the task being registered.
+ * @mgr contains the struct cred for the current binder process.
* Return 0 if permission is granted.
* @binder_transaction:
* Check whether @from is allowed to invoke a binder transaction call
* to @to.
- * @from contains the task_struct for the sending task.
- * @to contains the task_struct for the receiving task.
+ * @from contains the struct cred for the sending process.
+ * @to contains the struct cred for the receiving process.
* @binder_transfer_binder:
* Check whether @from is allowed to transfer a binder reference to @to.
- * @from contains the task_struct for the sending task.
- * @to contains the task_struct for the receiving task.
+ * @from contains the struct cred for the sending process.
+ * @to contains the struct cred for the receiving process.
* @binder_transfer_file:
* Check whether @from is allowed to transfer @file to @to.
- * @from contains the task_struct for the sending task.
+ * @from contains the struct cred for the sending process.
* @file contains the struct file being transferred.
- * @to contains the task_struct for the receiving task.
+ * @to contains the struct cred for the receiving process.
*
* @ptrace_access_check:
* Check permission before allowing the current process to trace the
@@ -1353,13 +1353,13 @@
* @ctxlen points to the place to put the length of @ctx.
*/
union security_list_options {
- int (*binder_set_context_mgr)(struct task_struct *mgr);
- int (*binder_transaction)(struct task_struct *from,
- struct task_struct *to);
- int (*binder_transfer_binder)(struct task_struct *from,
- struct task_struct *to);
- int (*binder_transfer_file)(struct task_struct *from,
- struct task_struct *to,
+ int (*binder_set_context_mgr)(const struct cred *mgr);
+ int (*binder_transaction)(const struct cred *from,
+ const struct cred *to);
+ int (*binder_transfer_binder)(const struct cred *from,
+ const struct cred *to);
+ int (*binder_transfer_file)(const struct cred *from,
+ const struct cred *to,
struct file *file);
int (*ptrace_access_check)(struct task_struct *child,
diff --git a/include/linux/security.h b/include/linux/security.h
index dab093af4ee8..1c8968a267c2 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -197,13 +197,13 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
extern int security_init(void);
/* Security operations */
-int security_binder_set_context_mgr(struct task_struct *mgr);
-int security_binder_transaction(struct task_struct *from,
- struct task_struct *to);
-int security_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to);
-int security_binder_transfer_file(struct task_struct *from,
- struct task_struct *to, struct file *file);
+int security_binder_set_context_mgr(const struct cred *mgr);
+int security_binder_transaction(const struct cred *from,
+ const struct cred *to);
+int security_binder_transfer_binder(const struct cred *from,
+ const struct cred *to);
+int security_binder_transfer_file(const struct cred *from,
+ const struct cred *to, struct file *file);
int security_ptrace_access_check(struct task_struct *child, unsigned int mode);
int security_ptrace_traceme(struct task_struct *parent);
int security_capget(struct task_struct *target,
@@ -424,25 +424,25 @@ static inline int security_init(void)
return 0;
}
-static inline int security_binder_set_context_mgr(struct task_struct *mgr)
+static inline int security_binder_set_context_mgr(const struct cred *mgr)
{
return 0;
}
-static inline int security_binder_transaction(struct task_struct *from,
- struct task_struct *to)
+static inline int security_binder_transaction(const struct cred *from,
+ const struct cred *to)
{
return 0;
}
-static inline int security_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to)
+static inline int security_binder_transfer_binder(const struct cred *from,
+ const struct cred *to)
{
return 0;
}
-static inline int security_binder_transfer_file(struct task_struct *from,
- struct task_struct *to,
+static inline int security_binder_transfer_file(const struct cred *from,
+ const struct cred *to,
struct file *file)
{
return 0;
diff --git a/security/security.c b/security/security.c
index 4fbe4e495c02..737a5985343c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -222,25 +222,25 @@ EXPORT_SYMBOL(unregister_lsm_notifier);
/* Security operations */
-int security_binder_set_context_mgr(struct task_struct *mgr)
+int security_binder_set_context_mgr(const struct cred *mgr)
{
return call_int_hook(binder_set_context_mgr, 0, mgr);
}
-int security_binder_transaction(struct task_struct *from,
- struct task_struct *to)
+int security_binder_transaction(const struct cred *from,
+ const struct cred *to)
{
return call_int_hook(binder_transaction, 0, from, to);
}
-int security_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to)
+int security_binder_transfer_binder(const struct cred *from,
+ const struct cred *to)
{
return call_int_hook(binder_transfer_binder, 0, from, to);
}
-int security_binder_transfer_file(struct task_struct *from,
- struct task_struct *to, struct file *file)
+int security_binder_transfer_file(const struct cred *from,
+ const struct cred *to, struct file *file)
{
return call_int_hook(binder_transfer_file, 0, from, to, file);
}
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 895d369bc410..9bb1d492f704 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2136,21 +2136,18 @@ static inline u32 open_file_to_av(struct file *file)
/* Hook functions begin here. */
-static int selinux_binder_set_context_mgr(struct task_struct *mgr)
+static int selinux_binder_set_context_mgr(const struct cred *mgr)
{
- u32 mysid = current_sid();
- u32 mgrsid = task_sid(mgr);
-
- return avc_has_perm(mysid, mgrsid, SECCLASS_BINDER,
+ return avc_has_perm(current_sid(), cred_sid(mgr), SECCLASS_BINDER,
BINDER__SET_CONTEXT_MGR, NULL);
}
-static int selinux_binder_transaction(struct task_struct *from,
- struct task_struct *to)
+static int selinux_binder_transaction(const struct cred *from,
+ const struct cred *to)
{
u32 mysid = current_sid();
- u32 fromsid = task_sid(from);
- u32 tosid = task_sid(to);
+ u32 fromsid = cred_sid(from);
+ u32 tosid = cred_sid(to);
int rc;
if (mysid != fromsid) {
@@ -2164,21 +2161,19 @@ static int selinux_binder_transaction(struct task_struct *from,
NULL);
}
-static int selinux_binder_transfer_binder(struct task_struct *from,
- struct task_struct *to)
+static int selinux_binder_transfer_binder(const struct cred *from,
+ const struct cred *to)
{
- u32 fromsid = task_sid(from);
- u32 tosid = task_sid(to);
-
- return avc_has_perm(fromsid, tosid, SECCLASS_BINDER, BINDER__TRANSFER,
+ return avc_has_perm(cred_sid(from), cred_sid(to),
+ SECCLASS_BINDER, BINDER__TRANSFER,
NULL);
}
-static int selinux_binder_transfer_file(struct task_struct *from,
- struct task_struct *to,
+static int selinux_binder_transfer_file(const struct cred *from,
+ const struct cred *to,
struct file *file)
{
- u32 sid = task_sid(to);
+ u32 sid = cred_sid(to);
struct file_security_struct *fsec = file->f_security;
struct dentry *dentry = file->f_path.dentry;
struct inode_security_struct *isec;
--
2.34.0.rc0.344.g81b53c2807-goog
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