This is a note to let you know that I've just added the patch titled
binder: fix race that allows malicious free of live buffer
to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From 7bada55ab50697861eee6bb7d60b41e68a961a9c Mon Sep 17 00:00:00 2001
From: Todd Kjos <tkjos(a)android.com>
Date: Tue, 6 Nov 2018 15:55:32 -0800
Subject: binder: fix race that allows malicious free of live buffer
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Malicious code can attempt to free buffers using the BC_FREE_BUFFER
ioctl to binder. There are protections against a user freeing a buffer
while in use by the kernel, however there was a window where
BC_FREE_BUFFER could be used to free a recently allocated buffer that
was not completely initialized. This resulted in a use-after-free
detected by KASAN with a malicious test program.
This window is closed by setting the buffer's allow_user_free attribute
to 0 when the buffer is allocated or when the user has previously freed
it instead of waiting for the caller to set it. The problem was that
when the struct buffer was recycled, allow_user_free was stale and set
to 1 allowing a free to go through.
Signed-off-by: Todd Kjos <tkjos(a)google.com>
Acked-by: Arve Hjønnevåg <arve(a)android.com>
Cc: stable <stable(a)vger.kernel.org> # 4.14
Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org>
---
drivers/android/binder.c | 21 ++++++++++++---------
drivers/android/binder_alloc.c | 16 ++++++----------
drivers/android/binder_alloc.h | 3 +--
3 files changed, 19 insertions(+), 21 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index cb30a524d16d..9f1000d2a40c 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2974,7 +2974,6 @@ static void binder_transaction(struct binder_proc *proc,
t->buffer = NULL;
goto err_binder_alloc_buf_failed;
}
- t->buffer->allow_user_free = 0;
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node;
@@ -3510,14 +3509,18 @@ static int binder_thread_write(struct binder_proc *proc,
buffer = binder_alloc_prepare_to_free(&proc->alloc,
data_ptr);
- if (buffer == NULL) {
- binder_user_error("%d:%d BC_FREE_BUFFER u%016llx no match\n",
- proc->pid, thread->pid, (u64)data_ptr);
- break;
- }
- if (!buffer->allow_user_free) {
- binder_user_error("%d:%d BC_FREE_BUFFER u%016llx matched unreturned buffer\n",
- proc->pid, thread->pid, (u64)data_ptr);
+ if (IS_ERR_OR_NULL(buffer)) {
+ if (PTR_ERR(buffer) == -EPERM) {
+ binder_user_error(
+ "%d:%d BC_FREE_BUFFER u%016llx matched unreturned or currently freeing buffer\n",
+ proc->pid, thread->pid,
+ (u64)data_ptr);
+ } else {
+ binder_user_error(
+ "%d:%d BC_FREE_BUFFER u%016llx no match\n",
+ proc->pid, thread->pid,
+ (u64)data_ptr);
+ }
break;
}
binder_debug(BINDER_DEBUG_FREE_BUFFER,
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 64fd96eada31..030c98f35cca 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -151,16 +151,12 @@ static struct binder_buffer *binder_alloc_prepare_to_free_locked(
else {
/*
* Guard against user threads attempting to
- * free the buffer twice
+ * free the buffer when in use by kernel or
+ * after it's already been freed.
*/
- if (buffer->free_in_progress) {
- binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
- "%d:%d FREE_BUFFER u%016llx user freed buffer twice\n",
- alloc->pid, current->pid,
- (u64)user_ptr);
- return NULL;
- }
- buffer->free_in_progress = 1;
+ if (!buffer->allow_user_free)
+ return ERR_PTR(-EPERM);
+ buffer->allow_user_free = 0;
return buffer;
}
}
@@ -500,7 +496,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
rb_erase(best_fit, &alloc->free_buffers);
buffer->free = 0;
- buffer->free_in_progress = 0;
+ buffer->allow_user_free = 0;
binder_insert_allocated_buffer_locked(alloc, buffer);
binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
"%d: binder_alloc_buf size %zd got %pK\n",
diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h
index 9ef64e563856..fb3238c74c8a 100644
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -50,8 +50,7 @@ struct binder_buffer {
unsigned free:1;
unsigned allow_user_free:1;
unsigned async_transaction:1;
- unsigned free_in_progress:1;
- unsigned debug_id:28;
+ unsigned debug_id:29;
struct binder_transaction *transaction;
--
2.19.2
Hello,
We ran automated tests on a recent commit from this kernel tree:
Kernel repo: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
Commit: be4bbf9fbca5 Linux 4.19.5-rc1
The results of these automated tests are provided below.
Overall result: PASSED
Patch merge: OK
Compile: OK
Kernel tests: OK
Please reply to this email if you have any questions about the tests that we
ran or if you have any suggestions on how to make future tests more effective.
,-. ,-.
( C ) ( K ) Continuous
`-',-.`-' Kernel
( I ) Integration
`-'
______________________________________________________________________________
Compile testing
---------------
We compiled the kernel for 2 architectures:
aarch64:
make options: make INSTALL_MOD_STRIP=1 -j56 targz-pkg
configuration: https://artifacts.cki-project.org/builds/aarch64/be4bbf9fbca5867a720f1f53c7…
x86_64:
make options: make INSTALL_MOD_STRIP=1 -j56 targz-pkg
configuration: https://artifacts.cki-project.org/builds/x86_64/be4bbf9fbca5867a720f1f53c7d…
Hardware testing
----------------
We booted each kernel and ran the following tests:
arm64:
/distribution/kpkginstall (boot test)
LTP lite - release 20180515
xfstests: ext4
xfstests: xfs
/kernel/misc/amtu
x86_64:
/distribution/kpkginstall (boot test)
LTP lite - release 20180515
xfstests: ext4
xfstests: xfs
/kernel/misc/amtu
Hi Greg,
Please apply commit 2278446e2b7c ("xhci: Fix USB3 NULL pointer dereference
at logical disconnect.") to v4.4.y. It fixes commit 44a182b9d177 ("xhci:
Fix use-after-free in xhci_free_virt_device"), which was applied to v4.4.y.
Thanks,
Guenter