This is a note to let you know that I've just added the patch titled
binder: fix UAF caused by faulty buffer cleanup
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
binder-fix-uaf-caused-by-faulty-buffer-cleanup.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From bdc1c5fac982845a58d28690cdb56db8c88a530d Mon Sep 17 00:00:00 2001
From: Carlos Llamas <cmllamas@xxxxxxxxxx>
Date: Fri, 5 May 2023 20:30:20 +0000
Subject: binder: fix UAF caused by faulty buffer cleanup
From: Carlos Llamas <cmllamas@xxxxxxxxxx>
commit bdc1c5fac982845a58d28690cdb56db8c88a530d upstream.
In binder_transaction_buffer_release() the 'failed_at' offset indicates
the number of objects to clean up. However, this function was changed by
commit 44d8047f1d87 ("binder: use standard functions to allocate fds"),
to release all the objects in the buffer when 'failed_at' is zero.
This introduced an issue when a transaction buffer is released without
any objects having been processed so far. In this case, 'failed_at' is
indeed zero yet it is misinterpreted as releasing the entire buffer.
This leads to use-after-free errors where nodes are incorrectly freed
and subsequently accessed. Such is the case in the following KASAN
report:
==================================================================
BUG: KASAN: slab-use-after-free in binder_thread_read+0xc40/0x1f30
Read of size 8 at addr ffff4faf037cfc58 by task poc/474
CPU: 6 PID: 474 Comm: poc Not tainted 6.3.0-12570-g7df047b3f0aa #5
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x94/0xec
show_stack+0x18/0x24
dump_stack_lvl+0x48/0x60
print_report+0xf8/0x5b8
kasan_report+0xb8/0xfc
__asan_load8+0x9c/0xb8
binder_thread_read+0xc40/0x1f30
binder_ioctl+0xd9c/0x1768
__arm64_sys_ioctl+0xd4/0x118
invoke_syscall+0x60/0x188
[...]
Allocated by task 474:
kasan_save_stack+0x3c/0x64
kasan_set_track+0x2c/0x40
kasan_save_alloc_info+0x24/0x34
__kasan_kmalloc+0xb8/0xbc
kmalloc_trace+0x48/0x5c
binder_new_node+0x3c/0x3a4
binder_transaction+0x2b58/0x36f0
binder_thread_write+0x8e0/0x1b78
binder_ioctl+0x14a0/0x1768
__arm64_sys_ioctl+0xd4/0x118
invoke_syscall+0x60/0x188
[...]
Freed by task 475:
kasan_save_stack+0x3c/0x64
kasan_set_track+0x2c/0x40
kasan_save_free_info+0x38/0x5c
__kasan_slab_free+0xe8/0x154
__kmem_cache_free+0x128/0x2bc
kfree+0x58/0x70
binder_dec_node_tmpref+0x178/0x1fc
binder_transaction_buffer_release+0x430/0x628
binder_transaction+0x1954/0x36f0
binder_thread_write+0x8e0/0x1b78
binder_ioctl+0x14a0/0x1768
__arm64_sys_ioctl+0xd4/0x118
invoke_syscall+0x60/0x188
[...]
==================================================================
In order to avoid these issues, let's always calculate the intended
'failed_at' offset beforehand. This is renamed and wrapped in a helper
function to make it clear and convenient.
Fixes: 32e9f56a96d8 ("binder: don't detect sender/target during buffer cleanup")
Reported-by: Zi Fan Tan <zifantan@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230505203020.4101154-1-cmllamas@xxxxxxxxxx
[cmllamas: resolve trivial conflict due to missing commit 9864bb4801331]
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/android/binder.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2270,24 +2270,23 @@ static void binder_deferred_fd_close(int
static void binder_transaction_buffer_release(struct binder_proc *proc,
struct binder_thread *thread,
struct binder_buffer *buffer,
- binder_size_t failed_at,
+ binder_size_t off_end_offset,
bool is_failure)
{
int debug_id = buffer->debug_id;
- binder_size_t off_start_offset, buffer_offset, off_end_offset;
+ binder_size_t off_start_offset, buffer_offset;
binder_debug(BINDER_DEBUG_TRANSACTION,
"%d buffer release %d, size %zd-%zd, failed at %llx\n",
proc->pid, buffer->debug_id,
buffer->data_size, buffer->offsets_size,
- (unsigned long long)failed_at);
+ (unsigned long long)off_end_offset);
if (buffer->target_node)
binder_dec_node(buffer->target_node, 1, 0);
off_start_offset = ALIGN(buffer->data_size, sizeof(void *));
- off_end_offset = is_failure && failed_at ? failed_at :
- off_start_offset + buffer->offsets_size;
+
for (buffer_offset = off_start_offset; buffer_offset < off_end_offset;
buffer_offset += sizeof(binder_size_t)) {
struct binder_object_header *hdr;
@@ -2447,6 +2446,21 @@ static void binder_transaction_buffer_re
}
}
+/* Clean up all the objects in the buffer */
+static inline void binder_release_entire_buffer(struct binder_proc *proc,
+ struct binder_thread *thread,
+ struct binder_buffer *buffer,
+ bool is_failure)
+{
+ binder_size_t off_end_offset;
+
+ off_end_offset = ALIGN(buffer->data_size, sizeof(void *));
+ off_end_offset += buffer->offsets_size;
+
+ binder_transaction_buffer_release(proc, thread, buffer,
+ off_end_offset, is_failure);
+}
+
static int binder_translate_binder(struct flat_binder_object *fp,
struct binder_transaction *t,
struct binder_thread *thread)
@@ -3930,7 +3944,7 @@ binder_free_buf(struct binder_proc *proc
binder_node_inner_unlock(buf_node);
}
trace_binder_transaction_buffer_release(buffer);
- binder_transaction_buffer_release(proc, thread, buffer, 0, is_failure);
+ binder_release_entire_buffer(proc, thread, buffer, is_failure);
binder_alloc_free_buf(&proc->alloc, buffer);
}
Patches currently in stable-queue which might be from cmllamas@xxxxxxxxxx are
queue-5.4/binder-fix-uaf-caused-by-faulty-buffer-cleanup.patch
