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

Thorsten Blum posted 1 patch 2 months ago
There is a newer version of this series
fs/smb/server/smb2pdu.c | 2 +-
fs/smb/server/smb2pdu.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
[PATCH] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()
Posted by Thorsten Blum 2 months ago 
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@linux.dev>
---
 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;
 
 struct srv_copychunk {
-- 
2.46.1
Re: [PATCH] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()
Posted by Tom Talpey 2 months ago 
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@linux.dev>
> ---
>   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.

The better fix would be to type the buffer contents properly, but that
will have protocol implications and should be thoroughly tested.

NAK on this change for now.

Tom.


>   struct srv_copychunk {
Re: [PATCH] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()
Posted by Thorsten Blum 2 months ago 
Hi Tom,

> On 24. Sep 2024, at 20:05, Tom Talpey <tom@talpey.com> 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@linux.dev>
>> ---
>>  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
Re: [PATCH] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()
Posted by Thorsten Blum 2 months ago 
On 24. Sep 2024, at 21:33, Thorsten Blum <thorsten.blum@linux.dev> wrote:
>> On 24. Sep 2024, at 20:05, Tom Talpey <tom@talpey.com> 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@linux.dev>
>>> ---
>>> 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);
> }

Never mind, I just realized that the pointer arithmetic takes the array
offset into account.

A srv_copychunk takes up 24 bytes and therefore 24 __u8[] slots. The
__counted_by annotation is essentially off by a factor of 24.

Thanks,
Thorsten
Re: [PATCH] ksmbd: Annotate struct copychunk_ioctl_req with __counted_by_le()
Posted by Tom Talpey 2 months ago 
On 9/24/2024 4:56 PM, Thorsten Blum wrote:
> On 24. Sep 2024, at 21:33, Thorsten Blum <thorsten.blum@linux.dev> wrote:
>>> On 24. Sep 2024, at 20:05, Tom Talpey <tom@talpey.com> 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@linux.dev>
>>>> ---
>>>> 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);
>> }
> 
> Never mind, I just realized that the pointer arithmetic takes the array
> offset into account.
> 
> A srv_copychunk takes up 24 bytes and therefore 24 __u8[] slots. The
> __counted_by annotation is essentially off by a factor of 24.

Right, and the fix is probably obvious, but the copychunk code has
yielded a few surprises in the past, so I'd really like to see any
change tested... Maybe Steve has a ready-to-go section in his set.

Tom.

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