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Message-ID: <20170422151412.GA14861@mail.hallyn.com>
Date: Sat, 22 Apr 2017 10:14:12 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: "Serge E. Hallyn" <serge@...lyn.com>,
Seth Forshee <seth.forshee@...onical.com>,
lkml <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
linux-security-module@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
Andreas Gruenbacher <agruenba@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
"Andrew G. Morgan" <morgan@...nel.org>
Subject: Re: [PATCH] Introduce v3 namespaced file capabilities
Quoting Eric W. Biederman (ebiederm@...ssion.com):
>
> "Serge E. Hallyn" <serge@...lyn.com> writes:
>
> Overall this looks quite reasonable.
>
> My only big concern was the lack of verifying of magic_etc. As without
Yes, I was relying too much on the size check.
> that the code might not be future compatible with new versions of the
> capability xattrs. It it tends to be nice to be able to boot old
> kernels when regression testing etc. Even if they can't make use of
> all of the features of a new filesystem.
That certainly was my intent.
> > diff --git a/fs/xattr.c b/fs/xattr.c
> > index 7e3317c..75cc65a 100644
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -170,12 +170,29 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
> > const void *value, size_t size, int flags)
> > {
> > struct inode *inode = dentry->d_inode;
> > - int error = -EAGAIN;
> > + int error;
> > + void *wvalue = NULL;
> > + size_t wsize = 0;
> > int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
> > XATTR_SECURITY_PREFIX_LEN);
> >
> > - if (issec)
> > + if (issec) {
> > inode->i_flags &= ~S_NOSEC;
> > +
> > + if (!strcmp(name, "security.capability")) {
> > + error = cap_setxattr_convert_nscap(dentry, value, size,
> > + &wvalue, &wsize);
> > + if (error < 0)
> > + return error;
> > + if (wvalue) {
> > + value = wvalue;
> > + size = wsize;
> > + }
> > + }
> > + }
> > +
> > + error = -EAGAIN;
> > +
>
> Why is the conversion in __vfs_setxattr_noperm and not in setattr as
> was done for posix_acl_fix_xattr_from_user?
I think I was thinking I wanted to catch all the vfs_setxattr operations,
but I don't think that's right. Moving to setxattr seems right. I'll
look around a bit more.
> > if (inode->i_opflags & IOP_XATTR) {
> > error = __vfs_setxattr(dentry, inode, name, value, size, flags);
> > if (!error) {
> > @@ -184,8 +201,10 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
> > size, flags);
> > }
> > } else {
> > - if (unlikely(is_bad_inode(inode)))
> > - return -EIO;
> > + if (unlikely(is_bad_inode(inode))) {
> > + error = -EIO;
> > + goto out;
> > + }
> > }
> > if (error == -EAGAIN) {
> > error = -EOPNOTSUPP;
> > @@ -200,10 +219,11 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
> > }
> > }
> >
> > +out:
> > + kfree(wvalue);
> > return error;
> > }
> >
> > -
> > int
> > vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> > size_t size, int flags)
>
> The rest of my comments I am going to express as an incremental diff.
> Using "security.capability" directly looks like a typo waiting to
> happen.
>
> You have an unnecessary include of linux/uidgid.h
>
> Missing version checks on the magic_etc field.
> And the wrong error code when the code deliberately refuses to return a
> capability.
Thanks, all looks good. Did you want to just squash these yourself and
move on, keep them as separate patches, or have me incorporate into mine
and resend?
> Eric
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 75cc65ac7ea9..f6d5ce3e1030 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -179,7 +179,7 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
> if (issec) {
> inode->i_flags &= ~S_NOSEC;
>
> - if (!strcmp(name, "security.capability")) {
> + if (!strcmp(name, XATTR_NAME_CAPS)) {
> error = cap_setxattr_convert_nscap(dentry, value, size,
> &wvalue, &wsize);
> if (error < 0)
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index b97343353a11..c47febf8448b 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -13,7 +13,6 @@
> #define _LINUX_CAPABILITY_H
>
> #include <uapi/linux/capability.h>
> -#include <linux/uidgid.h>
>
> #define _KERNEL_CAPABILITY_VERSION _LINUX_CAPABILITY_VERSION_3
> #define _KERNEL_CAPABILITY_U32S _LINUX_CAPABILITY_U32S_3
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 8abb9bf4ec17..32e32f437ef5 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -367,6 +367,7 @@ int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
> kuid_t kroot;
> uid_t root, mappedroot;
> char *tmpbuf = NULL;
> + struct vfs_cap_data *cap;
> struct vfs_ns_cap_data *nscap;
> struct dentry *dentry;
> struct user_namespace *fs_ns;
> @@ -379,14 +380,16 @@ int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
> return -EINVAL;
>
> size = sizeof(struct vfs_ns_cap_data);
> - ret = vfs_getxattr_alloc(dentry, "security.capability",
> + ret = vfs_getxattr_alloc(dentry, XATTR_NAME_CAPS,
> &tmpbuf, size, GFP_NOFS);
>
> if (ret < 0)
> return ret;
>
> fs_ns = inode->i_sb->s_user_ns;
> - if (ret == sizeof(struct vfs_cap_data)) {
> + cap = (struct vfs_cap_data *) tmpbuf;
> + if ((ret == sizeof(struct vfs_cap_data)) &&
> + (cap->magic_etc == cpu_to_le32(VFS_CAP_REVISION_2))) {
> /* If this is sizeof(vfs_cap_data) then we're ok with the
> * on-disk value, so return that. */
> if (alloc)
> @@ -394,7 +397,8 @@ int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
> else
> kfree(tmpbuf);
> return ret;
> - } else if (ret != sizeof(struct vfs_ns_cap_data)) {
> + } else if ((ret != sizeof(struct vfs_ns_cap_data)) ||
> + (cap->magic_etc != cpu_to_le32(VFS_CAP_REVISION_3))) {
> kfree(tmpbuf);
> return -EINVAL;
> }
> @@ -417,7 +421,7 @@ int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
>
> if (!rootid_owns_currentns(kroot)) {
> kfree(tmpbuf);
> - return -EOPNOTSUPP;
> + return -ENODATA;
> }
>
> /* This comes from a parent namespace. Return as a v2 capability */
> @@ -474,11 +478,17 @@ int cap_setxattr_convert_nscap(struct dentry *dentry, const void *value, size_t
> return -EINVAL;
> if (size != XATTR_CAPS_SZ_2 && size != XATTR_CAPS_SZ_3)
> return -EINVAL;
> + if ((size == XATTR_CAPS_SZ_2) &&
> + (cap->magic_etc != cpu_to_le32(VFS_CAP_REVISION_2)))
> + return -EINVAL;
> + if ((size == XATTR_CAPS_SZ_3) &&
> + (cap->magic_etc != cpu_to_le32(VFS_CAP_REVISION_3)))
> + return -EINVAL;
> if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
> return -EPERM;
> if (size == XATTR_CAPS_SZ_2)
> if (ns_capable(inode->i_sb->s_user_ns, CAP_SETFCAP))
> - // user is privileged, just write the v2
> + /* user is privileged, just write the v2 */
> return 0;
>
> rootid = rootid_from_xattr(value, size, task_ns);
> @@ -855,7 +865,10 @@ int cap_inode_setxattr(struct dentry *dentry, const char *name,
> sizeof(XATTR_SECURITY_PREFIX) - 1) != 0)
> return 0;
>
> - // For XATTR_NAME_CAPS the check will be done in __vfs_setxattr_noperm()
> + /*
> + * For XATTR_NAME_CAPS the check will be done in
> + * __vfs_setxattr_noperm()
> + */
> if (strcmp(name, XATTR_NAME_CAPS) == 0)
> return 0;
>
>
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