| Message ID | 20170405001206.GA58184@beast (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Apr 04 2017, 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> > --- > fs/nfs/namespace.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c > index 786f17580582..89f50bf12f52 100644 > --- a/fs/nfs/namespace.c > +++ b/fs/nfs/namespace.c > @@ -259,9 +259,10 @@ struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh, > if (page == NULL) > goto out; > devname = nfs_devname(dentry, page, PAGE_SIZE); > - mnt = (struct vfsmount *)devname; > - if (IS_ERR(devname)) > + if (IS_ERR(devname)) { > + mnt = ERR_PTR(PTR_ERR(devname)); Allow me to introduce you to ERR_CAST() /** * ERR_CAST - Explicitly cast an error-valued pointer to another pointer type * @ptr: The pointer to cast. * * Explicitly cast an error-valued pointer to another pointer type in such a * way as to make it clear that's what's going on. */ So: + mnt = ERR_CAST(devname); NeilBrown
On Tue, Apr 4, 2017 at 6:09 PM, NeilBrown <neilb@suse.com> wrote: > On Tue, Apr 04 2017, 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> >> --- >> fs/nfs/namespace.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c >> index 786f17580582..89f50bf12f52 100644 >> --- a/fs/nfs/namespace.c >> +++ b/fs/nfs/namespace.c >> @@ -259,9 +259,10 @@ struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh, >> if (page == NULL) >> goto out; >> devname = nfs_devname(dentry, page, PAGE_SIZE); >> - mnt = (struct vfsmount *)devname; >> - if (IS_ERR(devname)) >> + if (IS_ERR(devname)) { >> + mnt = ERR_PTR(PTR_ERR(devname)); > > Allow me to introduce you to ERR_CAST() Ah! Thank you, yes, that's precisely what I wanted. And only 10 lines away from where I was reading in err.h trying to find the right approach. *sigh* > /** > * ERR_CAST - Explicitly cast an error-valued pointer to another pointer type > * @ptr: The pointer to cast. > * > * Explicitly cast an error-valued pointer to another pointer type in such a > * way as to make it clear that's what's going on. > */ > > So: > + mnt = ERR_CAST(devname); I'll send a v2. :) -Kees
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c index 786f17580582..89f50bf12f52 100644 --- a/fs/nfs/namespace.c +++ b/fs/nfs/namespace.c @@ -259,9 +259,10 @@ struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh, if (page == NULL) goto out; devname = nfs_devname(dentry, page, PAGE_SIZE); - mnt = (struct vfsmount *)devname; - if (IS_ERR(devname)) + if (IS_ERR(devname)) { + mnt = ERR_PTR(PTR_ERR(devname)); goto free_page; + } mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata); free_page: free_page((unsigned long)page);
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> --- fs/nfs/namespace.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)