commit 3f489c2067c5824528212b0fc18b28d51332d906 upstream.
The mmap read lock is used during the shrinker's callback, which means
that using alloc->vma pointer isn't safe as it can race with munmap().
As of commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in
munmap") the mmap lock is downgraded after the vma has been isolated.
I was able to reproduce this issue by manually adding some delays and
triggering page reclaiming through the shrinker's debug sysfs. The
following KASAN report confirms the UAF:
==================================================================
BUG: KASAN: slab-use-after-free in zap_page_range_single+0x470/0x4b8
Read of size 8 at addr ffff356ed50e50f0 by task bash/478
CPU: 1 PID: 478 Comm: bash Not tainted 6.6.0-rc5-00055-g1c8b86a3799f-dirty #70
Hardware name: linux,dummy-virt (DT)
Call trace:
zap_page_range_single+0x470/0x4b8
binder_alloc_free_page+0x608/0xadc
__list_lru_walk_one+0x130/0x3b0
list_lru_walk_node+0xc4/0x22c
binder_shrink_scan+0x108/0x1dc
shrinker_debugfs_scan_write+0x2b4/0x500
full_proxy_write+0xd4/0x140
vfs_write+0x1ac/0x758
ksys_write+0xf0/0x1dc
__arm64_sys_write+0x6c/0x9c
Allocated by task 492:
kmem_cache_alloc+0x130/0x368
vm_area_alloc+0x2c/0x190
mmap_region+0x258/0x18bc
do_mmap+0x694/0xa60
vm_mmap_pgoff+0x170/0x29c
ksys_mmap_pgoff+0x290/0x3a0
__arm64_sys_mmap+0xcc/0x144
Freed by task 491:
kmem_cache_free+0x17c/0x3c8
vm_area_free_rcu_cb+0x74/0x98
rcu_core+0xa38/0x26d4
rcu_core_si+0x10/0x1c
__do_softirq+0x2fc/0xd24
Last potentially related work creation:
__call_rcu_common.constprop.0+0x6c/0xba0
call_rcu+0x10/0x1c
vm_area_free+0x18/0x24
remove_vma+0xe4/0x118
do_vmi_align_munmap.isra.0+0x718/0xb5c
do_vmi_munmap+0xdc/0x1fc
__vm_munmap+0x10c/0x278
__arm64_sys_munmap+0x58/0x7c
Fix this issue by performing instead a vma_lookup() which will fail to
find the vma that was isolated before the mmap lock downgrade. Note that
this option has better performance than upgrading to a mmap write lock
which would increase contention. Plus, mmap_write_trylock() has been
recently removed anyway.
Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Liam Howlett <liam.howlett@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231201172212.1813387-3-cmllamas@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[cmllamas: use find_vma() instead of vma_lookup() as commit ce6d42f2e4a2
is missing in v5.4. This only works because we check the vma against
our cached alloc->vma pointer. Also, unlock via up_read() instead of
mmap_read_unlock() as commit d8ed45c5dcd4 is also missing in v5.4.]
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
---
drivers/android/binder_alloc.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index f766e889d241..fd5e55db44c2 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -953,7 +953,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
goto err_mmget;
if (!down_read_trylock(&mm->mmap_sem))
goto err_down_read_mmap_sem_failed;
- vma = binder_alloc_get_vma(alloc);
+ vma = find_vma(mm, page_addr);
+ if (vma && vma != binder_alloc_get_vma(alloc))
+ goto err_invalid_vma;
list_lru_isolate(lru, item);
spin_unlock(lock);
@@ -979,6 +981,8 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
mutex_unlock(&alloc->mutex);
return LRU_REMOVED_RETRY;
+err_invalid_vma:
+ up_read(&mm->mmap_sem);
err_down_read_mmap_sem_failed:
mmput_async(mm);
err_mmget:
--
2.43.0.429.g432eaa2c6b-goog
