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    SubjectRe: [PATCH 6/6] sysctl: pass kernel pointers to ->proc_handler
    On Fri, Apr 17, 2020 at 11:17:18AM -0700, Matthew Wilcox wrote:
    > > if (error)
    > > - goto out;
    > > + goto out_free_buf;
    > >
    > > /* careful: calling conventions are nasty here */
    >
    > I think this comment can go now ;-)

    It actually long predates the set_fs that was only added for BPF,
    and goes back to:

    330d57fb98a91 ("[PATCH] Fix sysctl unregistration oops (CVE-2005-2709)")
    in the history.git tree.

    > > - } else {
    > > - error = table->proc_handler(table, write, buf, &count, ppos);
    > > - }
    > > + error = table->proc_handler(table, write, kbuf, &count, ppos);
    > > + if (error)
    > > + goto out_free_buf;
    > > +
    > > + error = -EFAULT;
    > > + if (copy_to_user(ubuf, kbuf, count))
    > > + goto out_free_buf;
    >
    > Can we skip this if !write? Indeed, don't we have to in case the user has
    > passed a pointer to a read-only memory page?

    Indeed.

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