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Message-Id: <20200714181638.45751-3-mic@digikod.net> Date: Tue, 14 Jul 2020 20:16:33 +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>, Mickaël Salaün <mickael.salaun@....gouv.fr>, 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@....gouv.fr>, 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 v6 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: Kees Cook <keescook@...omium.org> Acked-by: Mickaël Salaün <mic@...ikod.net> 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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