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Date:   Thu, 30 Dec 2021 10:41:51 +0100
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Stefan Roesch <shr@fb.com>, io-uring@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, kernel-team@fb.com,
        torvalds@linux-foundation.org
Subject: Re: [PATCH v10 2/5] fs: split off setxattr_copy and do_setxattr
 function from setxattr
Message-ID: <20211230094151.z7frfjxv3xhlgckx@wittgenstein>
References: <20211229203002.4110839-1-shr@fb.com>
 <20211229203002.4110839-3-shr@fb.com>
 <Yc0IHp2igNlXqyKV@zeniv-ca.linux.org.uk>
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On Thu, Dec 30, 2021 at 01:15:10AM +0000, Al Viro wrote:
> On Wed, Dec 29, 2021 at 12:29:59PM -0800, Stefan Roesch wrote:
> > +	if (ctx->size) {
> > +		if (ctx->size > XATTR_SIZE_MAX)
> >  			return -E2BIG;
> > -		kvalue = kvmalloc(size, GFP_KERNEL);
> > -		if (!kvalue)
> > +
> > +		ctx->kvalue = kvmalloc(ctx->size, GFP_KERNEL);
> > +		if (!ctx->kvalue)
> >  			return -ENOMEM;
> > -		if (copy_from_user(kvalue, value, size)) {
> > -			error = -EFAULT;
> > -			goto out;
> > +
> > +		if (copy_from_user(ctx->kvalue, ctx->value, ctx->size)) {
> > +			kvfree(ctx->kvalue);
> > +			return -EFAULT;
> 
> BTW, what's wrong with using vmemdup_user() here?

Nothing? It's simply timing paired with that specific code not needing
to be touched:

- in 2005 that code was kmalloc(GFP_KERNEL) + copy_from_user()
- in 2009 it was changed to memdup_user(GFP_USER)
- in 2012 it was changed to kvmalloc(GFP_KERNEL) + copy_from_user()

In 2018 you added vmemdup_user() and noone has updated that codepath. :)