[PATCH] Staging: exfat: Avoid use of strcpy

[PATCH] Staging: exfat: Avoid use of strcpy

[Sandro Volery]

Replaced strcpy with strscpy in exfat_core.c.

Signed-off-by: Sandro Volery <sandro@volery.com>
---
 drivers/staging/exfat/exfat_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/exfat/exfat_core.c b/drivers/staging/exfat/exfat_core.c
index da8c58149c35..c71b145e8a24 100644
--- a/drivers/staging/exfat/exfat_core.c
+++ b/drivers/staging/exfat/exfat_core.c
@@ -2964,7 +2964,7 @@ s32 resolve_path(struct inode *inode, char *path, struct chain_t *p_dir,
 	if (strlen(path) >= (MAX_NAME_LENGTH * MAX_CHARSET_SIZE))
 		return FFS_INVALIDPATH;
 
-	strcpy(name_buf, path);
+	strscpy(name_buf, path, sizeof(name_buf));
 
 	nls_cstring_to_uniname(sb, p_uniname, name_buf, &lossy);
 	if (lossy)
-- 
2.23.0

Re: [PATCH] Staging: exfat: Avoid use of strcpy

[Dan Carpenter]

On Wed, Sep 11, 2019 at 07:57:49AM +0200, Sandro Volery wrote:
> Replaced strcpy with strscpy in exfat_core.c.
> 
> Signed-off-by: Sandro Volery <sandro@volery.com>
> ---
>  drivers/staging/exfat/exfat_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/exfat/exfat_core.c b/drivers/staging/exfat/exfat_core.c
> index da8c58149c35..c71b145e8a24 100644
> --- a/drivers/staging/exfat/exfat_core.c
> +++ b/drivers/staging/exfat/exfat_core.c
> @@ -2964,7 +2964,7 @@ s32 resolve_path(struct inode *inode, char *path, struct chain_t *p_dir,
>  	if (strlen(path) >= (MAX_NAME_LENGTH * MAX_CHARSET_SIZE))
>  		return FFS_INVALIDPATH;
>  
> -	strcpy(name_buf, path);
> +	strscpy(name_buf, path, sizeof(name_buf));

It checked strlen() earlier so we know that it can't overflow but, oh
wow, the "name_buf" is a shared buffer.  wow wow wow.  This seems very
racy.

regards,
dan carpenter

Re: [PATCH] Staging: exfat: Avoid use of strcpy

[Rasmus Villemoes]

On 11/09/2019 10.41, Dan Carpenter wrote:
> On Wed, Sep 11, 2019 at 07:57:49AM +0200, Sandro Volery wrote:
>> Replaced strcpy with strscpy in exfat_core.c.
>>
>> Signed-off-by: Sandro Volery <sandro@volery.com>
>> ---
>>  drivers/staging/exfat/exfat_core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/staging/exfat/exfat_core.c b/drivers/staging/exfat/exfat_core.c
>> index da8c58149c35..c71b145e8a24 100644
>> --- a/drivers/staging/exfat/exfat_core.c
>> +++ b/drivers/staging/exfat/exfat_core.c
>> @@ -2964,7 +2964,7 @@ s32 resolve_path(struct inode *inode, char *path, struct chain_t *p_dir,
>>  	if (strlen(path) >= (MAX_NAME_LENGTH * MAX_CHARSET_SIZE))
>>  		return FFS_INVALIDPATH;
>>  
>> -	strcpy(name_buf, path);
>> +	strscpy(name_buf, path, sizeof(name_buf));
> 
> It checked strlen() earlier so we know that it can't overflow but, oh
> wow, the "name_buf" is a shared buffer.  wow wow wow.  This seems very
> racy.

Yeah, and note that the callers of resolve_path do seem to take a lock,
but that's not a global lock but a per-superblock (or
per-something-else) one... Obviously exfat should not rely on such a
single static buffer, but in the meantime, perhaps one should add a
name_buf_lock (though I don't know how long name_buf is actually in use,
so that needs checking).

Apart from the broken/lack of locking, it would be better to combine the
copying and length checking into a single check - i.e. do

  if (strscpy(name_buf, path, sizeof(name_buf)) < 0)
    return FFS_INVALIDPATH;

That's both more efficient and fixes the open-coding of sizeof(name_buf)
that is currently used in the if().

Rasmus