Subject: Re: [PATCH] sunrpc: fix uninitialized xprt_create_args structure

From: Hongling Zeng <[email-masked]>
Date: Wed, 03 Jun 2026 09:33:32 +0800

Hi Anna and Jeff,

   Thanks for the review!

   Regarding Anna's question about copying fields from the main xprt:

   Based on my analysis, these missing fields are not stored in
   struct rpc_xprt:
   - srcaddr: only passed during creation, not stored in xprt
   - bc_xps: not present in rpc_xprt (only bc_xprt is stored)
   - flags: not stored in xprt after creation

   Since these values are not available in the main xprt, we cannot
   copy them. Zero-initializing is the correct approach with the
   current design.

   Updated to v2 with designated initializer as suggested by Jeff.

   Thanks,
   Hongling

在 2026年06月02日 23:59, Anna Schumaker 写道:
> Hi Hongling,
>
> Thanks for the patch!
>
> On Tue, Jun 2, 2026, at 4:32 AM, Hongling Zeng wrote:
>> The xprt_create_args structure is allocated on the stack without
>> initialization in rpc_sysfs_xprt_switch_add_xprt_store(). While some
>> fields are manually populated, critical fields like srcaddr, bc_xps,
>> and flags contain uninitialized stack garbage.
>>
>> This can lead to:
>> 1. Kernel panic when xs_setup_xprt() dereferences garbage srcaddr
>> 2. Information leak if srcaddr points to sensitive stack data
>> 3. Unpredictable behavior if flags has random bits set
> I took a look through the transport setup function to see what they
> do when these fields are set to NULL, and it looks like thy do their
> best to choose a default value which might be different than the
> values set to the original transport that we are trying to clone.
>
> Can we instead set the missing fields in the xprt_create_args based
> on how the main xprt is configured?
>
> Thanks,
> Anna
>
>> The fix is to zero-initialize the structure to ensure all unused
>> fields are NULL/0, preventing the transport setup code from acting
>> on garbage data.
>>
>> Cc: [email-masked]
>> Signed-off-by: Hongling Zeng <[email-masked]>
>> ---
>>   net/sunrpc/sysfs.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/net/sunrpc/sysfs.c b/net/sunrpc/sysfs.c
>> index a90480f80154..0a99d0f1eb4c 100644
>> --- a/net/sunrpc/sysfs.c
>> +++ b/net/sunrpc/sysfs.c
>> @@ -333,6 +333,7 @@ static ssize_t
>> rpc_sysfs_xprt_switch_add_xprt_store(struct kobject *kobj,
>>   	if (!xprt_switch)
>>   		return 0;
>>
>> +	memset(&xprt_create_args, 0, sizeof(xprt_create_args));
>>   	xprt = rpc_xprt_switch_get_main_xprt(xprt_switch);
>>   	if (!xprt)
>>   		goto out;
>> -- 
>> 2.25.1