Re: [PATCH] greybus: Fix null pointer dereference in gb_operation_response_send()

From: Alex Elder
Date: Sun Oct 27 2024 - 10:00:59 EST


On 10/27/24 2:53 AM, Suraj Sonawane wrote:
Fix an issue detected by the Smatch static tool:
drivers/greybus/operation.c:852 gb_operation_response_send() error:
we previously assumed 'operation->response' could be null (see line 829)

There is no need for this. This is a case where the code is
doing something that is too involved for "smatch" to know
things are OK.

A unidirectional operation includes only a request message, but
no response message.

There are two cases:
- Unidirectional
- There is no response buffer
- There will be no call to gb_operation_response_alloc(),
because the operation is unidirectional.
- The result gets set with the errno value. If there's
an error (there shouldn't be), -EIO is returned.
- We return 0 early, because it's a unidirectional operation.
- Not unidirectional
- If there is a response, we attempt to allocate one. If that
fails, we return -ENOMEM early.
- Otherwise there *is* a response (it was successfully allocated)
- The result is set
- It is not unidirectional, so we get a reference to the operation,
add it to the active list (or skip to the end if not connected)
- We record the result in the response header. This is the line in
question, but we know the response pointer is good.
- We send the response.
- On error, we drop or references and return the error code.

-Alex



The issue occurs because 'operation->response' may be null if the
response allocation fails at line 829. However, the code tries to
access 'operation->response->header' at line 852 without checking if
it was successfully allocated. This can cause a crash if 'response'
is null.

To fix this, add a check to ensure 'operation->response' is not null
before accessing its header. If the response is null, log an error
message and return -ENOMEM to stop further processing, preventing
any crashes or undefined behavior.

Signed-off-by: Suraj Sonawane <surajsonawane0215@xxxxxxxxx>
---
drivers/greybus/operation.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/greybus/operation.c b/drivers/greybus/operation.c
index 8459e9bc0..521899fbc 100644
--- a/drivers/greybus/operation.c
+++ b/drivers/greybus/operation.c
@@ -849,7 +849,13 @@ static int gb_operation_response_send(struct gb_operation *operation,
goto err_put;
/* Fill in the response header and send it */
- operation->response->header->result = gb_operation_errno_map(errno);
+ if (operation->response) {
+ operation->response->header->result = gb_operation_errno_map(errno);
+ } else {
+ dev_err(&connection->hd->dev, "failed to allocate response\n");
+ ret = -ENOMEM;
+ goto err_put_active;
+ }
ret = gb_message_send(operation->response, GFP_KERNEL);
if (ret)