Re: [PATCH] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()

[Thorsten Blum <thorsten.blum@xxxxxxxxx>]

Hi Tom,

> On 24. Sep 2024, at 20:05, Tom Talpey <tom@xxxxxxxxxx> wrote:
> On 9/24/2024 6:22 AM, Thorsten Blum wrote:
>> Add the __counted_by_le compiler attribute to the flexible array member
>> Chunks to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
>> CONFIG_FORTIFY_SOURCE.
>> Read Chunks[0] after checking that ChunkCount is not 0.
>> Compile-tested only.
>> Signed-off-by: Thorsten Blum <thorsten.blum@xxxxxxxxx>
>> ---
>>  fs/smb/server/smb2pdu.c | 2 +-
>>  fs/smb/server/smb2pdu.h | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
>> index 461c4fc682ac..0670bdf3e167 100644
>> --- a/fs/smb/server/smb2pdu.c
>> +++ b/fs/smb/server/smb2pdu.c
>> @@ -7565,7 +7565,6 @@ static int fsctl_copychunk(struct ksmbd_work *work,
>>   ci_rsp->TotalBytesWritten =
>>   cpu_to_le32(ksmbd_server_side_copy_max_total_size());
>>  - chunks = (struct srv_copychunk *)&ci_req->Chunks[0];
>>   chunk_count = le32_to_cpu(ci_req->ChunkCount);
>>   if (chunk_count == 0)
>>   goto out;
>> @@ -7579,6 +7578,7 @@ static int fsctl_copychunk(struct ksmbd_work *work,
>>   return -EINVAL;
>>   }
>>  + chunks = (struct srv_copychunk *)&ci_req->Chunks[0];
>>   for (i = 0; i < chunk_count; i++) {
>>   if (le32_to_cpu(chunks[i].Length) == 0 ||
>>      le32_to_cpu(chunks[i].Length) > ksmbd_server_side_copy_max_chunk_size())
>> diff --git a/fs/smb/server/smb2pdu.h b/fs/smb/server/smb2pdu.h
>> index 73aff20e22d0..f01121dbf358 100644
>> --- a/fs/smb/server/smb2pdu.h
>> +++ b/fs/smb/server/smb2pdu.h
>> @@ -194,7 +194,7 @@ struct copychunk_ioctl_req {
>>   __le64 ResumeKey[3];
>>   __le32 ChunkCount;
>>   __le32 Reserved;
>> - __u8 Chunks[]; /* array of srv_copychunk */
>> + __u8 Chunks[] __counted_by_le(ChunkCount); /* array of srv_copychunk */
>>  } __packed;
>>  
> 
> This isn't correct. The u8 is just a raw buffer, copychunk structs are
> marshaled into it, and they're 24 bytes each.

Hm, I see.

How does this for-loop work then? It iterates over ci_req->ChunkCount
and expects a srv_copychunk at each ci_req->Chunks[i]?

for (i = 0; i < chunk_count; i++) {
	if (le32_to_cpu(chunks[i].Length) == 0 ||
	    le32_to_cpu(chunks[i].Length) > ksmbd_server_side_copy_max_chunk_size())
		break;
	total_size_written += le32_to_cpu(chunks[i].Length);
}

Thanks,
Thorsten