From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiggers3@gmail.com (Eric Biggers) Date: Sat, 3 Jun 2017 22:47:46 -0700 Subject: [kernel-hardening] Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM In-Reply-To: References: <20170603055351.16080-1-matt@nmatt.com> <20170603063354.GJ6365@ZenIV.linux.org.uk> Message-ID: <20170604054746.GC12095@zzz> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org On Sun, Jun 04, 2017 at 01:24:13AM -0400, Matt Brown wrote: > On 06/03/2017 02:33 AM, Al Viro wrote: > > On Sat, Jun 03, 2017 at 01:53:51AM -0400, Matt Brown wrote: > > > > > +static int tpe_bprm_set_creds(struct linux_binprm *bprm) > > > +{ > > > + struct file *file = bprm->file; > > > + struct inode *inode = d_backing_inode(file->f_path.dentry->d_parent); > > > + struct inode *file_inode = d_backing_inode(file->f_path.dentry); > > > > Bloody wonderful. Do tell, what *does* prevent a race with rename(2) here, > > somehow making sure that your 'inode' won't get freed right under you? > > > > Good catch. How does this look: > > spin_lock(&inode->i_lock); > spin_lock(&file_inode->i_lock); > if (global_nonroot(inode->i_uid) && !uid_eq(inode->i_uid, cred->uid)) > reason1 = "directory not owned by user"; > else if (inode->i_mode & 0002) > reason1 = "file in world-writable directory"; > else if ((inode->i_mode & 0020) && global_nonroot_gid(inode->i_gid)) > reason1 = "file in group-writable directory"; > else if (file_inode->i_mode & 0002) > reason1 = "file is world-writable"; > spin_unlock(&inode->i_lock); > spin_unlock(&file_inode->i_lock); > > and likewise for other places in the code? No, it needs to take a reference on the parent dentry before using it, using dget_parent(), I think, and then dropping it later with dput(). Taking i_lock isn't needed. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html