Re: [PATCH v1] seq_file: Fix overflow condition in seq_commit

[Arun KS]

Hi Al Viro,

On Tue, Aug 20, 2013 at 1:06 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Aug 20, 2013 at 12:51:56PM +0530, Arun KS wrote:
>
>> d_path expects the pathname to be less than 64 bytes. If its more than
>> 64, it returns -ENAMETOOLONG.
>
> ?!?!?  d_path() does not expect anything of that sort - it can very
> well produce names much longer, without ENAMETOOLONG.
>
>> char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
>>                         const char *fmt, ...)
>> {
>>         va_list args;
>>         char temp[64];
>>         int sz;
>>
>>         va_start(args, fmt);
>>         sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
>>         va_end(args);
>>
>>         if (sz > sizeof(temp) || sz > buflen)
>>                 return ERR_PTR(-ENAMETOOLONG);
>>
>>         buffer += buflen - sz;
>>         return memcpy(buffer, temp, sz);
>> }
>
> Aha.  _That_ is a bug, all right - dynamic_dname() is simply not suitable
> for that kind of uses.  ashmem.c is certainly abusing shmem_file_setup();
> feeding that kind of mess as dentry name is a Bad Idea(tm).  Anyway,
> I'd suggest this for a fix:
>
>         va_list args;
>         size_t sz;
>         va_start(args, fmt);
>         sz = vsnprintf(NULL, 0, fmt, args) + 1;
>         va_end(args);
>         if (sz > buflen)
>                 return ERR_PTR(-ENAMETOOLONG);
>         va_start(args, fmt);
>         buffer += buflen - sz;
>         vsprintf(buffer, fmt, args);
>         va_end(args);
>         return buffer;
>
> Either right in dynamic_dname(), or as possibly_fucking_long_dname(),
> to be used by shmem.c...

This fixes the problem.

Thanks,
Arun
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/