This is a note to let you know that I've just added the patch titled
android: binder: fix the race mmap and alloc_new_buf_locked
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 da1b9564e85b1d7baf66cbfabcab27e183a1db63 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Thu, 23 Aug 2018 14:29:56 +0900
Subject: android: binder: fix the race mmap and alloc_new_buf_locked
There is RaceFuzzer report like below because we have no lock to close
below the race between binder_mmap and binder_alloc_new_buf_locked.
To close the race, let's use memory barrier so that if someone see
alloc->vma is not NULL, alloc->vma_vm_mm should be never NULL.
(I didn't add stable mark intentionallybecause standard android
userspace libraries that interact with binder (libbinder & libhwbinder)
prevent the mmap/ioctl race. - from Todd)
"
Thread interleaving:
CPU0 (binder_alloc_mmap_handler) CPU1 (binder_alloc_new_buf_locked)
===== =====
// drivers/android/binder_alloc.c
// #L718 (v4.18-rc3)
alloc->vma = vma;
// drivers/android/binder_alloc.c
// #L346 (v4.18-rc3)
if (alloc->vma == NULL) {
...
// alloc->vma is not NULL at this point
return ERR_PTR(-ESRCH);
}
...
// #L438
binder_update_page_range(alloc, 0,
(void *)PAGE_ALIGN((uintptr_t)buffer->data),
end_page_addr);
// In binder_update_page_range() #L218
// But still alloc->vma_vm_mm is NULL here
if (need_mm && mmget_not_zero(alloc->vma_vm_mm))
alloc->vma_vm_mm = vma->vm_mm;
Crash Log:
==================================================================
BUG: KASAN: null-ptr-deref in __atomic_add_unless include/asm-generic/atomic-instrumented.h:89 [inline]
BUG: KASAN: null-ptr-deref in atomic_add_unless include/linux/atomic.h:533 [inline]
BUG: KASAN: null-ptr-deref in mmget_not_zero include/linux/sched/mm.h:75 [inline]
BUG: KASAN: null-ptr-deref in binder_update_page_range+0xece/0x18e0 drivers/android/binder_alloc.c:218
Write of size 4 at addr 0000000000000058 by task syz-executor0/11184
CPU: 1 PID: 11184 Comm: syz-executor0 Not tainted 4.18.0-rc3 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x16e/0x22c lib/dump_stack.c:113
kasan_report_error mm/kasan/report.c:352 [inline]
kasan_report+0x163/0x380 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x140/0x1a0 mm/kasan/kasan.c:267
kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
__atomic_add_unless include/asm-generic/atomic-instrumented.h:89 [inline]
atomic_add_unless include/linux/atomic.h:533 [inline]
mmget_not_zero include/linux/sched/mm.h:75 [inline]
binder_update_page_range+0xece/0x18e0 drivers/android/binder_alloc.c:218
binder_alloc_new_buf_locked drivers/android/binder_alloc.c:443 [inline]
binder_alloc_new_buf+0x467/0xc30 drivers/android/binder_alloc.c:513
binder_transaction+0x125b/0x4fb0 drivers/android/binder.c:2957
binder_thread_write+0xc08/0x2770 drivers/android/binder.c:3528
binder_ioctl_write_read.isra.39+0x24f/0x8e0 drivers/android/binder.c:4456
binder_ioctl+0xa86/0xf34 drivers/android/binder.c:4596
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x154/0xd40 fs/ioctl.c:686
ksys_ioctl+0x94/0xb0 fs/ioctl.c:701
__do_sys_ioctl fs/ioctl.c:708 [inline]
__se_sys_ioctl fs/ioctl.c:706 [inline]
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:706
do_syscall_64+0x167/0x4b0 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
"
Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: Martijn Coenen <maco@xxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/android/binder_alloc.c | 43 +++++++++++++++++++++++++++-------
1 file changed, 35 insertions(+), 8 deletions(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 3f3b7b253445..64fd96eada31 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -332,6 +332,35 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
return vma ? -ENOMEM : -ESRCH;
}
+
+static inline void binder_alloc_set_vma(struct binder_alloc *alloc,
+ struct vm_area_struct *vma)
+{
+ if (vma)
+ alloc->vma_vm_mm = vma->vm_mm;
+ /*
+ * If we see alloc->vma is not NULL, buffer data structures set up
+ * completely. Look at smp_rmb side binder_alloc_get_vma.
+ * We also want to guarantee new alloc->vma_vm_mm is always visible
+ * if alloc->vma is set.
+ */
+ smp_wmb();
+ alloc->vma = vma;
+}
+
+static inline struct vm_area_struct *binder_alloc_get_vma(
+ struct binder_alloc *alloc)
+{
+ struct vm_area_struct *vma = NULL;
+
+ if (alloc->vma) {
+ /* Look at description in binder_alloc_set_vma */
+ smp_rmb();
+ vma = alloc->vma;
+ }
+ return vma;
+}
+
static struct binder_buffer *binder_alloc_new_buf_locked(
struct binder_alloc *alloc,
size_t data_size,
@@ -348,7 +377,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
size_t size, data_offsets_size;
int ret;
- if (alloc->vma == NULL) {
+ if (!binder_alloc_get_vma(alloc)) {
binder_alloc_debug(BINDER_DEBUG_USER_ERROR,
"%d: binder_alloc_buf, no vma\n",
alloc->pid);
@@ -723,9 +752,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
buffer->free = 1;
binder_insert_free_buffer(alloc, buffer);
alloc->free_async_space = alloc->buffer_size / 2;
- barrier();
- alloc->vma = vma;
- alloc->vma_vm_mm = vma->vm_mm;
+ binder_alloc_set_vma(alloc, vma);
mmgrab(alloc->vma_vm_mm);
return 0;
@@ -754,10 +781,10 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
int buffers, page_count;
struct binder_buffer *buffer;
- BUG_ON(alloc->vma);
-
buffers = 0;
mutex_lock(&alloc->mutex);
+ BUG_ON(alloc->vma);
+
while ((n = rb_first(&alloc->allocated_buffers))) {
buffer = rb_entry(n, struct binder_buffer, rb_node);
@@ -900,7 +927,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc)
*/
void binder_alloc_vma_close(struct binder_alloc *alloc)
{
- WRITE_ONCE(alloc->vma, NULL);
+ binder_alloc_set_vma(alloc, NULL);
}
/**
@@ -935,7 +962,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
index = page - alloc->pages;
page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE;
- vma = alloc->vma;
+ vma = binder_alloc_get_vma(alloc);
if (vma) {
if (!mmget_not_zero(alloc->vma_vm_mm))
goto err_mmget;
--
2.18.0
