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authorTodd Kjos <tkjos@google.com>2020-06-22 13:07:15 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-06-23 07:54:46 +0200
commitd35d3660e065b69fdb8bf512f3d899f350afce52 (patch)
treea2f298acf05e3edd57bc2a5401fcc8aabe39e965 /drivers/android
parent48778464bb7d346b47157d21ffde2af6b2d39110 (diff)
downloadlinux-d35d3660e065b69fdb8bf512f3d899f350afce52.tar.bz2
binder: fix null deref of proc->context
The binder driver makes the assumption proc->context pointer is invariant after initialization (as documented in the kerneldoc header for struct proc). However, in commit f0fe2c0f050d ("binder: prevent UAF for binderfs devices II") proc->context is set to NULL during binder_deferred_release(). Another proc was in the middle of setting up a transaction to the dying process and crashed on a NULL pointer deref on "context" which is a local set to &proc->context: new_ref->data.desc = (node == context->binder_context_mgr_node) ? 0 : 1; Here's the stack: [ 5237.855435] Call trace: [ 5237.855441] binder_get_ref_for_node_olocked+0x100/0x2ec [ 5237.855446] binder_inc_ref_for_node+0x140/0x280 [ 5237.855451] binder_translate_binder+0x1d0/0x388 [ 5237.855456] binder_transaction+0x2228/0x3730 [ 5237.855461] binder_thread_write+0x640/0x25bc [ 5237.855466] binder_ioctl_write_read+0xb0/0x464 [ 5237.855471] binder_ioctl+0x30c/0x96c [ 5237.855477] do_vfs_ioctl+0x3e0/0x700 [ 5237.855482] __arm64_sys_ioctl+0x78/0xa4 [ 5237.855488] el0_svc_common+0xb4/0x194 [ 5237.855493] el0_svc_handler+0x74/0x98 [ 5237.855497] el0_svc+0x8/0xc The fix is to move the kfree of the binder_device to binder_free_proc() so the binder_device is freed when we know there are no references remaining on the binder_proc. Fixes: f0fe2c0f050d ("binder: prevent UAF for binderfs devices II") Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Todd Kjos <tkjos@google.com> Cc: stable <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20200622200715.114382-1-tkjos@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/android')
-rw-r--r--drivers/android/binder.c14
1 files changed, 7 insertions, 7 deletions
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index e47c8a4c83db..f50c5f182bb5 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4686,8 +4686,15 @@ static struct binder_thread *binder_get_thread(struct binder_proc *proc)
static void binder_free_proc(struct binder_proc *proc)
{
+ struct binder_device *device;
+
BUG_ON(!list_empty(&proc->todo));
BUG_ON(!list_empty(&proc->delivered_death));
+ device = container_of(proc->context, struct binder_device, context);
+ if (refcount_dec_and_test(&device->ref)) {
+ kfree(proc->context->name);
+ kfree(device);
+ }
binder_alloc_deferred_release(&proc->alloc);
put_task_struct(proc->tsk);
binder_stats_deleted(BINDER_STAT_PROC);
@@ -5406,7 +5413,6 @@ static int binder_node_release(struct binder_node *node, int refs)
static void binder_deferred_release(struct binder_proc *proc)
{
struct binder_context *context = proc->context;
- struct binder_device *device;
struct rb_node *n;
int threads, nodes, incoming_refs, outgoing_refs, active_transactions;
@@ -5423,12 +5429,6 @@ static void binder_deferred_release(struct binder_proc *proc)
context->binder_context_mgr_node = NULL;
}
mutex_unlock(&context->context_mgr_node_lock);
- device = container_of(proc->context, struct binder_device, context);
- if (refcount_dec_and_test(&device->ref)) {
- kfree(context->name);
- kfree(device);
- }
- proc->context = NULL;
binder_inner_proc_lock(proc);
/*
* Make sure proc stays alive after we