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Message-ID: <87a6z1m0u1.fsf@x220.int.ebiederm.org> Date: Tue, 11 Aug 2020 14:36:38 -0500 From: ebiederm@...ssion.com (Eric W. Biederman) To: Mickaël Salaün <mic@...ikod.net> Cc: linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Christian Brauner <christian.brauner@...ntu.com>, Christian Heimes <christian@...hon.org>, Daniel Borkmann <daniel@...earbox.net>, Deven Bowers <deven.desai@...ux.microsoft.com>, Dmitry Vyukov <dvyukov@...gle.com>, Eric Biggers <ebiggers@...nel.org>, Eric Chiang <ericchiang@...gle.com>, Florian Weimer <fweimer@...hat.com>, James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>, Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>, Michael Kerrisk <mtk.manpages@...il.com>, Mimi Zohar <zohar@...ux.ibm.com>, Philippe Trébuchet <philippe.trebuchet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, Thibaut Sautereau <thibaut.sautereau@...p-os.org>, Vincent Strubel <vincent.strubel@....gouv.fr>, kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH v7 3/7] exec: Move path_noexec() check earlier Mickaël Salaün <mic@...ikod.net> writes: > From: Kees Cook <keescook@...omium.org> > > The path_noexec() check, like the regular file check, was happening too > late, letting LSMs see impossible execve()s. Check it earlier as well > in may_open() and collect the redundant fs/exec.c path_noexec() test > under the same robustness comment as the S_ISREG() check. > > My notes on the call path, and related arguments, checks, etc: A big question arises, that I think someone already asked. Why perform this test in may_open directly instead of moving it into inode_permission. That way the code can be shared with faccessat, and any other code path that wants it? That would look to provide a more maintainable kernel. Eric > do_open_execat() > struct open_flags open_exec_flags = { > .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, > .acc_mode = MAY_EXEC, > ... > do_filp_open(dfd, filename, open_flags) > path_openat(nameidata, open_flags, flags) > file = alloc_empty_file(open_flags, current_cred()); > do_open(nameidata, file, open_flags) > may_open(path, acc_mode, open_flag) > /* new location of MAY_EXEC vs path_noexec() test */ > inode_permission(inode, MAY_OPEN | acc_mode) > security_inode_permission(inode, acc_mode) > vfs_open(path, file) > do_dentry_open(file, path->dentry->d_inode, open) > security_file_open(f) > open() > /* old location of path_noexec() test */ > > Signed-off-by: Mickaël Salaün <mic@...ikod.net> > Signed-off-by: Kees Cook <keescook@...omium.org> > Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org > --- > fs/exec.c | 12 ++++-------- > fs/namei.c | 4 ++++ > 2 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index bdc6a6eb5dce..4eea20c27b01 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) > * and check again at the very end too. > */ > error = -EACCES; > - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) > - goto exit; > - > - if (path_noexec(&file->f_path)) > + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > + path_noexec(&file->f_path))) > goto exit; > > fsnotify_open(file); > @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags) > * and check again at the very end too. > */ > err = -EACCES; > - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode))) > - goto exit; > - > - if (path_noexec(&file->f_path)) > + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) || > + path_noexec(&file->f_path))) > goto exit; > > err = deny_write_access(file); > diff --git a/fs/namei.c b/fs/namei.c > index a559ad943970..ddc9b25540fe 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag) > return -EACCES; > flag &= ~O_TRUNC; > break; > + case S_IFREG: > + if ((acc_mode & MAY_EXEC) && path_noexec(path)) > + return -EACCES; > + break; > } > > error = inode_permission(inode, MAY_OPEN | acc_mode);
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