From: Petko Manolov <petkan@mip-labs.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
James Morris <jmorris@namei.org>,
linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
Mimi Zohar <zohar@linux.vnet.ibm.com>
Subject: Re: linux-next: manual merge of the security tree with the vfs tree
Date: Thu, 31 Dec 2015 12:45:35 +0200 [thread overview]
Message-ID: <20151231104535.GA5555@localhost> (raw)
In-Reply-To: <20151231043019.GD9938@ZenIV.linux.org.uk>
On 15-12-31 04:30:19, Al Viro wrote:
> On Thu, Dec 31, 2015 at 03:24:53PM +1100, Stephen Rothwell wrote:
> > Hi James,
> >
> > Today's linux-next merge of the security tree got a conflict in:
> >
> > security/integrity/ima/ima_fs.c
> >
> > between commit:
> >
> > 3bc8f29b149e ("new helper: memdup_user_nul()")
> >
> > from the vfs tree and commit:
> >
> > 38d859f991f3 ("IMA: policy can now be updated multiple times")
> >
> > from the security tree.
> >
> > I fixed it up (hopefully, see below) and can carry the fix as necessary
> > (no action is required).
>
> > + res = mutex_lock_interruptible(&ima_write_mutex);
> > + if (res)
> > + return res;
> >
> > if (datalen >= PAGE_SIZE)
> > datalen = PAGE_SIZE - 1;
> >
> > /* No partial writes. */
> > + result = -EINVAL;
> > if (*ppos != 0)
> > - return -EINVAL;
> > + goto out;
> >
> > - result = -ENOMEM;
> > - data = kmalloc(datalen + 1, GFP_KERNEL);
> > - if (!data)
> > - goto out;
> > -
> > - *(data + datalen) = '\0';
> > -
> > - result = -EFAULT;
> > - if (copy_from_user(data, buf, datalen))
> > + data = memdup_user_nul(buf, datalen);
> > - if (IS_ERR(data))
> > - return PTR_ERR(data);
> > ++ if (IS_ERR(data)) {
> > ++ result = PTR_ERR(data);
> > + goto out;
> > ++ }
>
> Why do it in this order? With or without opencoding memdup_user_nul(),
> what's the point of taking the mutex before copying the data from
> userland? All it achieves is holding it longer, over the area that
> needs no exclusion whatsoever.
I introduced the write mutex when ima_write_policy() stopped being serialized by
other means. Come to think about it the semaphore could be taken right before
copy_from_user() so it is my fault, not Stephen's.
The patch, however, leaves out a bug where free without allocation can occur.
Look at *ppos evaluation. Instead of "goto out" it should be "return -EINVAL;".
This requires the mutex lock to be moved down, though.
cheers,
Petko
next prev parent reply other threads:[~2015-12-31 10:45 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-31 4:24 linux-next: manual merge of the security tree with the vfs tree Stephen Rothwell
2015-12-31 4:30 ` Al Viro
2015-12-31 10:45 ` Petko Manolov [this message]
2016-01-01 4:34 ` Al Viro
2016-01-01 17:29 ` Petko Manolov
2016-01-01 17:41 ` [PATCH] ima_write_policy() optimizations; kbuild test robot
2016-01-04 1:37 ` linux-next: manual merge of the security tree with the vfs tree Mimi Zohar
2016-01-04 1:55 ` Stephen Rothwell
-- strict thread matches above, loose matches on Subject: below --
2019-08-12 4:44 Stephen Rothwell
2015-05-13 4:39 Stephen Rothwell
2015-05-13 4:26 Stephen Rothwell
2014-12-10 2:47 Stephen Rothwell
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20151231104535.GA5555@localhost \
--to=petkan@mip-labs.com \
--cc=jmorris@namei.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-next@vger.kernel.org \
--cc=sfr@canb.auug.org.au \
--cc=viro@ZenIV.linux.org.uk \
--cc=zohar@linux.vnet.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).