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binder: use cred instead of task for selinux checks

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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@vger.kernel.org # 5.14 (need backport for earlier stables)
Fixes: 79af73079d ("Add security hooks to binder and implement the hooks for SELinux.")
Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Todd Kjos <tkjos@google.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Todd Kjos 2021-10-12 09:56:13 -07:00 • committed by Paul Moore
parent 29bc22ac5e
commit 52f8869337
6 changed files with 54 additions and 76 deletions
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14
include/linux/lsm_hooks.h
View file

@ -1313,22 +1313,22 @@
*
* @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