From: Todd Kjos <tkjos@google.com> To: tkjos@google.com, gregkh@linuxfoundation.org, christian@brauner.io, arve@android.com, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, maco@google.com Cc: joel@joelfernandes.org, kernel-team@android.com Subject: [PATCH] binder: fix null deref of proc->context Date: Mon, 22 Jun 2020 13:07:15 -0700 [thread overview] Message-ID: <20200622200715.114382-1-tkjos@google.com> (raw) 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") Signed-off-by: Todd Kjos <tkjos@google.com> --- drivers/android/binder.c | 14 +++++++------- 1 file 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 -- 2.27.0.111.gc72c7da667-goog
WARNING: multiple messages have this Message-ID (diff)
From: Todd Kjos <tkjos@google.com> To: tkjos@google.com, gregkh@linuxfoundation.org, christian@brauner.io, arve@android.com, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, maco@google.com Cc: joel@joelfernandes.org, kernel-team@android.com Subject: [PATCH] binder: fix null deref of proc->context Date: Mon, 22 Jun 2020 13:07:15 -0700 [thread overview] Message-ID: <20200622200715.114382-1-tkjos@google.com> (raw) 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") Signed-off-by: Todd Kjos <tkjos@google.com> --- drivers/android/binder.c | 14 +++++++------- 1 file 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 -- 2.27.0.111.gc72c7da667-goog _______________________________________________ devel mailing list devel@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
next reply other threads:[~2020-06-22 20:07 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-22 20:07 Todd Kjos [this message] 2020-06-22 20:07 ` [PATCH] binder: fix null deref of proc->context Todd Kjos 2020-06-22 20:09 ` Christian Brauner 2020-06-22 20:09 ` Christian Brauner 2020-06-22 20:18 ` Todd Kjos 2020-06-22 20:18 ` Todd Kjos 2020-06-22 20:59 ` Todd Kjos 2020-06-22 20:59 ` Todd Kjos 2020-06-23 5:22 ` Greg Kroah-Hartman 2020-06-23 5:22 ` Greg Kroah-Hartman 2020-06-23 8:50 ` Dan Carpenter 2020-06-23 8:50 ` Dan Carpenter 2020-06-23 9:04 ` Christian Brauner 2020-06-23 9:04 ` Christian Brauner 2020-06-23 10:13 ` Dan Carpenter 2020-06-23 10:13 ` Dan Carpenter 2020-06-23 13:54 ` Joel Fernandes 2020-06-23 13:54 ` Joel Fernandes
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