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Message-Id: <20200723171227.446711-3-mic@digikod.net>
Date: Thu, 23 Jul 2020 19:12:22 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: linux-kernel@...r.kernel.org
Cc: Mickaël Salaün <mic@...ikod.net>,
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: [PATCH v7 2/7] exec: Move S_ISREG() check earlier
From: Kees Cook <keescook@...omium.org>
The execve(2)/uselib(2) syscalls have always rejected non-regular
files. Recently, it was noticed that a deadlock was introduced when trying
to execute pipes, as the S_ISREG() test was happening too late. This was
fixed in commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files
during execve()"), but it was added after inode_permission() had already
run, which meant LSMs could see bogus attempts to execute non-regular
files.
Move the test into the other inode type checks (which already look
for other pathological conditions[1]). Since there is no need to use
FMODE_EXEC while we still have access to "acc_mode", also switch the
test to MAY_EXEC.
Also include a comment with the redundant S_ISREG() checks at the end of
execve(2)/uselib(2) to note that they are present to avoid any mistakes.
My notes on the call path, and related arguments, checks, etc:
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 S_ISREG() 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)
/* old location of FMODE_EXEC vs S_ISREG() test */
security_file_open(f)
open()
[1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/
Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Signed-off-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org
---
fs/exec.c | 14 ++++++++++++--
fs/namei.c | 6 ++++--
fs/open.c | 6 ------
3 files changed, 16 insertions(+), 10 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index d7c937044d10..bdc6a6eb5dce 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -141,8 +141,13 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
if (IS_ERR(file))
goto out;
+ /*
+ * may_open() has already checked for this, so it should be
+ * impossible to trip now. But we need to be extra cautious
+ * and check again at the very end too.
+ */
error = -EACCES;
- if (!S_ISREG(file_inode(file)->i_mode))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
goto exit;
if (path_noexec(&file->f_path))
@@ -886,8 +891,13 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
if (IS_ERR(file))
goto out;
+ /*
+ * may_open() has already checked for this, so it should be
+ * impossible to trip now. But we need to be extra cautious
+ * and check again at the very end too.
+ */
err = -EACCES;
- if (!S_ISREG(file_inode(file)->i_mode))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
goto exit;
if (path_noexec(&file->f_path))
diff --git a/fs/namei.c b/fs/namei.c
index 72d4219c93ac..a559ad943970 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2849,16 +2849,18 @@ static int may_open(const struct path *path, int acc_mode, int flag)
case S_IFLNK:
return -ELOOP;
case S_IFDIR:
- if (acc_mode & MAY_WRITE)
+ if (acc_mode & (MAY_WRITE | MAY_EXEC))
return -EISDIR;
break;
case S_IFBLK:
case S_IFCHR:
if (!may_open_dev(path))
return -EACCES;
- /*FALLTHRU*/
+ fallthrough;
case S_IFIFO:
case S_IFSOCK:
+ if (acc_mode & MAY_EXEC)
+ return -EACCES;
flag &= ~O_TRUNC;
break;
}
diff --git a/fs/open.c b/fs/open.c
index 6cd48a61cda3..623b7506a6db 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -784,12 +784,6 @@ static int do_dentry_open(struct file *f,
return 0;
}
- /* Any file opened for execve()/uselib() has to be a regular file. */
- if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) {
- error = -EACCES;
- goto cleanup_file;
- }
-
if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
error = get_write_access(inode);
if (unlikely(error))
--
2.27.0
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