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[v2,01/20] NFS: Avoid cross-structure casting

Message ID 1495829844-69341-2-git-send-email-keescook@chromium.org (mailing list archive)
State New, archived
Headers show

Commit Message

Kees Cook May 26, 2017, 8:17 p.m. UTC 
When the call to nfs_devname() fails, the error path attempts to retain
the error via the mnt variable, but this requires a cast across very
different types (char * to struct vfsmount *), which the upcoming
structure layout randomization plugin flags as being potentially
dangerous in the face of randomization. This is a false positive, but
what this code actually wants to do is retain the error value, so this
patch explicitly sets it, instead of using what seems to be an
unexpected cast.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>
---
 fs/nfs/namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Christoph Hellwig May 28, 2017, 7:53 a.m. UTC | #1 
On Fri, May 26, 2017 at 01:17:05PM -0700, Kees Cook wrote:
> When the call to nfs_devname() fails, the error path attempts to retain
> the error via the mnt variable, but this requires a cast across very
> different types (char * to struct vfsmount *), which the upcoming
> structure layout randomization plugin flags as being potentially
> dangerous in the face of randomization. This is a false positive, but
> what this code actually wants to do is retain the error value, so this
> patch explicitly sets it, instead of using what seems to be an
> unexpected cast.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

And I think we should get this (and the other cast patches) in ASAP,
independent of the fat of the randstruct plugin.
Kees Cook May 28, 2017, 4:55 p.m. UTC | #2 
On Sun, May 28, 2017 at 12:53 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Fri, May 26, 2017 at 01:17:05PM -0700, Kees Cook wrote:
>> When the call to nfs_devname() fails, the error path attempts to retain
>> the error via the mnt variable, but this requires a cast across very
>> different types (char * to struct vfsmount *), which the upcoming
>> structure layout randomization plugin flags as being potentially
>> dangerous in the face of randomization. This is a false positive, but
>> what this code actually wants to do is retain the error value, so this
>> patch explicitly sets it, instead of using what seems to be an
>> unexpected cast.
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>
>
> Looks good:
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
>
> And I think we should get this (and the other cast patches) in ASAP,
> independent of the fat of the randstruct plugin.

Should I send a pull request to Linus for these for v4.12?

-Kees
diff mbox

Patch

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index 1a224a33a6c2..e5686be67be8 100644
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -246,7 +246,7 @@  struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh,
 
 	devname = nfs_devname(dentry, page, PAGE_SIZE);
 	if (IS_ERR(devname))
-		mnt = (struct vfsmount *)devname;
+		mnt = ERR_CAST(devname);
 	else
 		mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata);