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BACKPORT: binder: use euid from cred instead of using task

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Save the 'struct cred' associated with a binder process
at initial open to avoid potential race conditions
when converting to an euid.

Set a transaction's sender_euid from the 'struct cred'
saved at binder_open() instead of looking up the euid
from the binder proc's 'struct task'. This ensures
the euid is associated with the security context that
of the task that opened binder.

Cc: stable@vger.kernel.org # 4.4+
Fixes: 457b9a6f09 ("Staging: android: add binder driver")
Signed-off-by: Todd Kjos <tkjos@google.com>
Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Suggested-by: Jann Horn <jannh@google.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Bug: 200688826
(cherry picked from commit 29bc22ac5e5bc63275e850f0c8fc549e3d0e306b)
[ refactored to avoid changing KMI: struct binder_proc ]
Change-Id: Icaf996a7f5543b7d6943dff3cbe89bfc3614044c
This commit is contained in:
Todd Kjos
2021-10-12 09:56:12 -07:00
parent 7e2fbdaeab
commit d492977395
2 changed files with 32 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
drivers/android/binder.c
View File

@@ -2842,7 +2842,7 @@ static void binder_transaction(struct binder_proc *proc,
t->from = thread;
else
t->from = NULL;
t->sender_euid = task_euid(proc->tsk);
t->sender_euid = binder_get_cred(proc)->euid;
t->to_proc = target_proc;
t->to_thread = target_thread;
t->code = tr->code;
@@ -4486,6 +4486,8 @@ static struct binder_thread *binder_get_thread(struct binder_proc *proc)
static void binder_free_proc(struct binder_proc *proc)
{
struct binder_device *device;
struct binder_proc_ext *eproc =
container_of(proc, struct binder_proc_ext, proc);
BUG_ON(!list_empty(&proc->todo));
BUG_ON(!list_empty(&proc->delivered_death));
@@ -4499,8 +4501,9 @@ static void binder_free_proc(struct binder_proc *proc)
}
binder_alloc_deferred_release(&proc->alloc);
put_task_struct(proc->tsk);
put_cred(eproc->cred);
binder_stats_deleted(BINDER_STAT_PROC);
kfree(proc);
kfree(eproc);
}
static void binder_free_thread(struct binder_thread *thread)
@@ -5187,6 +5190,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
static int binder_open(struct inode *nodp, struct file *filp)
{
struct binder_proc *proc, *itr;
struct binder_proc_ext *eproc;
struct binder_device *binder_dev;
struct binderfs_info *info;
struct dentry *binder_binderfs_dir_entry_proc = NULL;
@@ -5195,13 +5199,15 @@ static int binder_open(struct inode *nodp, struct file *filp)
binder_debug(BINDER_DEBUG_OPEN_CLOSE, "%s: %d:%d\n", __func__,
current->group_leader->pid, current->pid);
proc = kzalloc(sizeof(*proc), GFP_KERNEL);
eproc = kzalloc(sizeof(*eproc), GFP_KERNEL);
proc = &eproc->proc;
if (proc == NULL)
return -ENOMEM;
spin_lock_init(&proc->inner_lock);
spin_lock_init(&proc->outer_lock);
get_task_struct(current->group_leader);
proc->tsk = current->group_leader;
eproc->cred = get_cred(filp->f_cred);
INIT_LIST_HEAD(&proc->todo);
init_waitqueue_head(&proc->freeze_wait);
if (binder_supported_policy(current->policy)) {

23
drivers/android/binder_internal.h
View File

@@ -473,6 +473,29 @@ struct binder_proc {
bool oneway_spam_detection_enabled;
};
/**
* struct binder_proc_ext - binder process bookkeeping
* @proc: element for binder_procs list
* @cred struct cred associated with the `struct file`
* in binder_open()
* (invariant after initialized)
*
* Extended binder_proc -- needed to add the "cred" field without
* changing the KMI for binder_proc.
*/
struct binder_proc_ext {
struct binder_proc proc;
const struct cred *cred;
};
static inline const struct cred *binder_get_cred(struct binder_proc *proc)
{
struct binder_proc_ext *eproc;
eproc = container_of(proc, struct binder_proc_ext, proc);
return eproc->cred;
}
/**
* struct binder_thread - binder thread bookkeeping
* @proc: binder process for this thread