linux-kernel - [PATCH 1/5] exec: Call cap_bprm_set_creds directly from prepare

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Date:   Sat, 09 May 2020 14:40:53 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Rob Landley <rob@...dley.net>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        <linux-fsdevel@...r.kernel.org>, Al Viro <viro@...IV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 1/5] exec: Call cap_bprm_set_creds directly from prepare_binprm


The function cap_bprm_set_creds is the only instance of
security_bprm_set_creds that does something for the primary executable
file and for every interpreter the rest of the implementations of
security_bprm_set_creds do something only for the primary executable
file even if that file is a shell script.

The function cap_bprm_set_creds is also special in that it is called
even when CONFIG_SECURITY is unset.

So calling cap_bprm_set_creds separately to make these two cases explicit,
and allow future changes to take advantages of these differences
to simplify the code.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/exec.c                | 4 ++++
 include/linux/security.h | 2 +-
 security/commoncap.c     | 1 -
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index b0620d5ebc66..765bfd51a546 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1641,6 +1641,10 @@ int prepare_binprm(struct linux_binprm *bprm)
 		return retval;
 	bprm->called_set_creds = 1;
 
+	retval = cap_bprm_set_creds(bprm);
+	if (retval)
+		return retval;
+
 	memset(bprm->buf, 0, BINPRM_BUF_SIZE);
 	return kernel_read(bprm->file, bprm->buf, BINPRM_BUF_SIZE, &pos);
 }
diff --git a/include/linux/security.h b/include/linux/security.h
index a8d9310472df..c1aa1638429a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -571,7 +571,7 @@ static inline int security_vm_enough_memory_mm(struct mm_struct *mm, long pages)
 
 static inline int security_bprm_set_creds(struct linux_binprm *bprm)
 {
-	return cap_bprm_set_creds(bprm);
+	return 0;
 }
 
 static inline int security_bprm_check(struct linux_binprm *bprm)
diff --git a/security/commoncap.c b/security/commoncap.c
index f4ee0ae106b2..3757988abe42 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -1346,7 +1346,6 @@ static struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
 	LSM_HOOK_INIT(capget, cap_capget),
 	LSM_HOOK_INIT(capset, cap_capset),
-	LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds),
 	LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
 	LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
 	LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),
-- 
2.25.0