binder: don't detect sender/target during buffer cleanup

PATCH In review Todd Kjos 3 participants 4 messages Oct 15, 2021 – Nov 2, 2021 Android drivers

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Todd Kjos

author

2021-10-15 23:38 UTC #0 lore raw

PATCH 1/1 binder: don't detect sender/target during buffer cleanup

When freeing txn buffers, binder_transaction_buffer_release() attempts to detect whether the current context is the target by comparing current->group_leader to proc->tsk. This is an unreliable test. Instead explicitly pass an 'is_failure' boolean.

Detecting the sender was being used as a way to tell if the transaction failed to be sent. When cleaning up after failing to send a transaction, there is no need to close the fds associated with a BINDER_TYPE_FDA object. Now 'is_failure' can be used to accurately detect this case.

Fixes 44d8047f1d87 ("binder: use standard functions to allocate fds")

Signed-off-by Todd Kjos <[email protected]>

---
 drivers/android/binder.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

drivers/android/binder.c +7 -7

index 9edacc8b9768..fe4c3b49eec1 100644
@@ -1870,7 +1870,7 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
 		binder_dec_node(buffer->target_node, 1, 0);
 
 	off_start_offset = ALIGN(buffer->data_size, sizeof(void *));
-	off_end_offset = is_failure ? failed_at :
+	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)) {

@@ -1956,9 +1956,8 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
 			binder_size_t fd_buf_size;
 			binder_size_t num_valid;
 
-			if (proc->tsk != current->group_leader) {
+			if (is_failure) {
 				/*
-				 * Nothing to do if running in sender context
 				 * The fd fixups have not been applied so no
 				 * fds need to be closed.
 				 */

@@ -3185,6 +3184,7 @@ static void binder_transaction(struct binder_proc *proc,
  * binder_free_buf() - free the specified buffer
  * @proc:	binder proc that owns buffer
  * @buffer:	buffer to be freed
+ * @is_failure:	failed to send transaction
  *
  * If buffer for an async transaction, enqueue the next async
  * transaction from the node.

@@ -3194,7 +3194,7 @@ static void binder_transaction(struct binder_proc *proc,
 static void
 binder_free_buf(struct binder_proc *proc,
 		struct binder_thread *thread,
-		struct binder_buffer *buffer)
+		struct binder_buffer *buffer, bool is_failure)
 {
 	binder_inner_proc_lock(proc);
 	if (buffer->transaction) {

@@ -3222,7 +3222,7 @@ 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, false);
+	binder_transaction_buffer_release(proc, thread, buffer, 0, is_failure);
 	binder_alloc_free_buf(&proc->alloc, buffer);
 }

@@ -3424,7 +3424,7 @@ static int binder_thread_write(struct binder_proc *proc,
 				     proc->pid, thread->pid, (u64)data_ptr,
 				     buffer->debug_id,
 				     buffer->transaction ? "active" : "finished");
-			binder_free_buf(proc, thread, buffer);
+			binder_free_buf(proc, thread, buffer, false);
 			break;
 		}

@@ -4117,7 +4117,7 @@ static int binder_thread_read(struct binder_proc *proc,
 			buffer->transaction = NULL;
 			binder_cleanup_transaction(t, "fd fixups failed",
 						   BR_FAILED_REPLY);
-			binder_free_buf(proc, thread, buffer);
+			binder_free_buf(proc, thread, buffer, true);
 			binder_debug(BINDER_DEBUG_FAILED_TRANSACTION,
 				     "%d:%d %stransaction %d fd fixups failed %d/%d, line %d\n",
 				     proc->pid, thread->pid,

Signature · 1 line

2.33.0.1079.g6e70778dc9-goog

Christian Brauner

Acked-by on v1 1/1

2021-10-18 10:35 UTC #1 lore raw

Quoted 11 lines · Todd Kjos

When freeing txn buffers, binder_transaction_buffer_release() attempts to detect whether the current context is the target by comparing current->group_leader to proc->tsk. This is an unreliable test. Instead explicitly pass an 'is_failure' boolean.
Detecting the sender was being used as a way to tell if the transaction failed to be sent. When cleaning up after failing to send a transaction, there is no need to close the fds associated with a BINDER_TYPE_FDA object. Now 'is_failure' can be used to accurately detect this case.

Quoted 3 lines

Fixes 44d8047f1d87 ("binder: use standard functions to allocate fds")
Signed-off-by Todd Kjos <[email protected]>
---

Looks good to me.

Acked-by Christian Brauner <[email protected]>

Dan Carpenter

2021-11-02 13:24 UTC #2 lore raw

In reply to Todd Kjos

Quoted 11 lines · Todd Kjos

When freeing txn buffers, binder_transaction_buffer_release() attempts to detect whether the current context is the target by comparing current->group_leader to proc->tsk. This is an unreliable test. Instead explicitly pass an 'is_failure' boolean.
Detecting the sender was being used as a way to tell if the transaction failed to be sent. When cleaning up after failing to send a transaction, there is no need to close the fds associated with a BINDER_TYPE_FDA object. Now 'is_failure' can be used to accurately detect this case.

It's really hard for me to understand what this bug looks like to the user? Is it a memory leak or do we free the wrong thing?

regards,
dan carpenter

Todd Kjos

author

2021-11-02 15:12 UTC #3 lore raw

Quoted 14 lines · Dan Carpenter

Quoted 11 lines · Todd Kjos
When freeing txn buffers, binder_transaction_buffer_release() attempts to detect whether the current context is the target by comparing current->group_leader to proc->tsk. This is an unreliable test. Instead explicitly pass an 'is_failure' boolean.
Detecting the sender was being used as a way to tell if the transaction failed to be sent. When cleaning up after failing to send a transaction, there is no need to close the fds associated with a BINDER_TYPE_FDA object. Now 'is_failure' can be used to accurately detect this case.

Quoted 2 lines

It's really hard for me to understand what this bug looks like to the user? Is it a memory leak or do we free the wrong thing?

It is a difficult case to hit (impossible for "well-behaved" processes), but it could result in file descriptors being closed when they shouldn't be.

Quoted 7 lines

regards,
dan carpenter
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