Smatch printed a warning:
	arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
	__memcpy() 'dctx->buf' too small (16 vs u32max)

It's caused because Smatch marks 'link_len' as untrusted since it comes
from sscanf(). Add a check to ensure that 'link_len' is not larger than
the size of the 'link_str' buffer.

Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
---
 fs/cifs/link.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/cifs/link.c b/fs/cifs/link.c
index 852e54e..ebfedae 100644
--- a/fs/cifs/link.c
+++ b/fs/cifs/link.c
@@ -85,6 +85,9 @@
 	if (rc != 1)
 		return -EINVAL;
 
+	if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
+		return -EINVAL;
+
 	rc = symlink_hash(link_len, link_str, md5_hash);
 	if (rc) {
 		cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
-- 
1.8.3.1

Wouldn't it be easier and clearer to do the compare vs the maximum len ie

if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)

instead of

if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)

since buf_len is  CIFS_MF_SYMLINK_FILE_SIZE and looking at link.c line
26 and 27 this means we can use CIFS_MF_SYMLINK_LINK_OFFSET for the
comparison:

#define CIFS_MF_SYMLINK_LINK_MAXLEN (1024)
#define CIFS_MF_SYMLINK_FILE_SIZE \
        (CIFS_MF_SYMLINK_LINK_OFFSET + CIFS_MF_SYMLINK_LINK_MAXLEN)

On Tue, Apr 12, 2022 at 1:01 AM Harshit Mogalapalli
<harshit.m.mogalapalli@oracle.com> wrote:
>
> Smatch printed a warning:
>         arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
>         __memcpy() 'dctx->buf' too small (16 vs u32max)
>
> It's caused because Smatch marks 'link_len' as untrusted since it comes
> from sscanf(). Add a check to ensure that 'link_len' is not larger than
> the size of the 'link_str' buffer.
>
> Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
> ---
>  fs/cifs/link.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/cifs/link.c b/fs/cifs/link.c
> index 852e54e..ebfedae 100644
> --- a/fs/cifs/link.c
> +++ b/fs/cifs/link.c
> @@ -85,6 +85,9 @@
>         if (rc != 1)
>                 return -EINVAL;
>
> +       if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
> +               return -EINVAL;
> +
>         rc = symlink_hash(link_len, link_str, md5_hash);
>         if (rc) {
>                 cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
> --
> 1.8.3.1
>


-- 
Thanks,

Steve

Hi Steve,
On 13/04/22 4:02 am, Steve French wrote:
> Wouldn't it be easier and clearer to do the compare vs the maximum len ie
> 
> if (link_len > CIFS_MF_SYMLINK_LINK_MAXLEN)
> 
Yes, thats cleaner. Will send a v2 patch.

Thanks,
Harshit
> instead of
> 
> if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
> 
> since buf_len is  CIFS_MF_SYMLINK_FILE_SIZE and looking at link.c line
> 26 and 27 this means we can use CIFS_MF_SYMLINK_LINK_OFFSET for the
> comparison:
> 
> #define CIFS_MF_SYMLINK_LINK_MAXLEN (1024)
> #define CIFS_MF_SYMLINK_FILE_SIZE \
>          (CIFS_MF_SYMLINK_LINK_OFFSET + CIFS_MF_SYMLINK_LINK_MAXLEN)
> 
> On Tue, Apr 12, 2022 at 1:01 AM Harshit Mogalapalli
> <harshit.m.mogalapalli@oracle.com> wrote:
>>
>> Smatch printed a warning:
>>          arch/x86/crypto/poly1305_glue.c:198 poly1305_update_arch() error:
>>          __memcpy() 'dctx->buf' too small (16 vs u32max)
>>
>> It's caused because Smatch marks 'link_len' as untrusted since it comes
>> from sscanf(). Add a check to ensure that 'link_len' is not larger than
>> the size of the 'link_str' buffer.
>>
>> Fixes: c69c1b6eaea1 ("cifs: implement CIFSParseMFSymlink()")
>> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
>> ---
>>   fs/cifs/link.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/fs/cifs/link.c b/fs/cifs/link.c
>> index 852e54e..ebfedae 100644
>> --- a/fs/cifs/link.c
>> +++ b/fs/cifs/link.c
>> @@ -85,6 +85,9 @@
>>          if (rc != 1)
>>                  return -EINVAL;
>>
>> +       if (link_len > buf_len - CIFS_MF_SYMLINK_LINK_OFFSET)
>> +               return -EINVAL;
>> +
>>          rc = symlink_hash(link_len, link_str, md5_hash);
>>          if (rc) {
>>                  cifs_dbg(FYI, "%s: MD5 hash failure: %d\n", __func__, rc);
>> --
>> 1.8.3.1
>>
> 
>