Re: RFC: pwritev2 regression test for invalid flags

[Jon Derrick <jonathan.derrick@intel.com>]

Hi Zanella,

On 06/15/2017 04:10 PM, Adhemerval Zanella wrote:
> After the issue with LO_HI_LONG definition on x86_64-linux-gnu, I planed to add 
> this patch to check the above patch for correct check for invalid flags (which
> would also have show this issue with LO_HI_LONG being used on p{read,write}v2).
> 
> However it seems to trigger what I think it is a kernel bug on version that
> provides p{read,write}v, where preadv2 does fails with EOPNOTSUPP but
> pwritev2 does not.  For instance, on x86_64-linux-gnu-x32 and i686-linux-gnu
> (4.10.0-21-generic/x86_64):

It looks like the issue is that you are going through the compat_writev
path, which for some reason discards the flags parameter.

Can you apply the patch below to your kernel?
diff --git a/fs/read_write.c b/fs/read_write.c
index c4f88af..f77eb22 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1210,7 +1210,7 @@ static size_t compat_writev(struct file *file,
        if (!(file->f_mode & FMODE_CAN_WRITE))
                goto out;

-       ret = compat_do_readv_writev(WRITE, file, vec, vlen, pos, 0);
+       ret = compat_do_readv_writev(WRITE, file, vec, vlen, pos, flags);

 out:
        if (ret > 0)