On Fri, May 5, 2023 at 1:30 PM Carlos Llamas cmllamas@google.com wrote:
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@google.com Cc: stable@vger.kernel.org Signed-off-by: Carlos Llamas cmllamas@google.com
Acked-by: Todd Kjos tkjos@google.com
v2: rename 'failed_at' to 'off_end_offsets' and drop the now unecessary comments after the rename per Todd's feedback.
drivers/android/binder.c | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index fb56bfc45096..8fb7672021ee 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -1934,24 +1934,23 @@ static void binder_deferred_fd_close(int fd) 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;@@ -2111,6 +2110,21 @@ static void binder_transaction_buffer_release(struct binder_proc *proc, } }
+/* 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) @@ -2806,7 +2820,7 @@ static int binder_proc_transaction(struct binder_transaction *t, t_outdated->buffer = NULL; buffer->transaction = NULL; trace_binder_transaction_update_buffer_release(buffer);
binder_transaction_buffer_release(proc, NULL, buffer, 0, 0);
binder_release_entire_buffer(proc, NULL, buffer, false); binder_alloc_free_buf(&proc->alloc, buffer); kfree(t_outdated); binder_stats_deleted(BINDER_STAT_TRANSACTION);@@ -3775,7 +3789,7 @@ 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);}
-- 2.40.1.521.gf1e218fcd8-goog