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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     <linux-kernel@vger.kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Rob Landley <rob@landley.net>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        <linux-fsdevel@vger.kernel.org>, Al Viro <viro@ZenIV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        linux-security-module@vger.kernel.org,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Andy Lutomirski <luto@amacapital.net>
References: <87h7wujhmz.fsf@x220.int.ebiederm.org>
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Date:   Thu, 28 May 2020 10:49:44 -0500
In-Reply-To: <87k10wysqz.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's
        message of "Thu, 28 May 2020 10:38:28 -0500")
Message-ID: <87y2pcvz3b.fsf_-_@x220.int.ebiederm.org>
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Subject: [PATCH 09/11] exec: In bprm_fill_uid only set per_clear when honoring suid or sgid
Sender: linux-kernel-owner@vger.kernel.org
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It makes no sense to set active_per_clear when the kernel decides not
to honor the executables setuid or or setgid bits.  Instead set
active_per_clear when the kernel actually decides to honor the suid or
sgid permission bits of an executable.

As far as I can tell this was the intended behavior but with the
ptrace logic hiding out in security/commcap.c:cap_bprm_apply_creds I
believe it was just overlooked that the setuid or setgid operation
could be cancelled.

History Tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Fixes: 1bb0fa189c6a ("[PATCH] NX: clean up legacy binary support")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/exec.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index af108ecf9632..347dade4bc54 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1634,15 +1634,16 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
 	need_cap = bprm->unsafe & LSM_UNSAFE_SHARE ||
 		!ptracer_capable(current, new->user_ns);
 
-	if (mode & S_ISUID) {
+	if ((mode & S_ISUID) &&
+	    (!need_cap || ns_capable(new->user_ns, CAP_SETUID))) {
 		bprm->per_clear = 1;
-		if (!need_cap || ns_capable(new->user_ns, CAP_SETUID))
-			new->suid = new->fsuid = new->euid = uid;
+		new->suid = new->fsuid = new->euid = uid;
 	}
-	if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
+
+	if (((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) &&
+	    (!need_cap || ns_capable(new->user_ns, CAP_SETGID))) {
 		bprm->per_clear = 1;
-		if (!need_cap || ns_capable(new->user_ns, CAP_SETGID))
-			new->sgid = new->fsgid = new->egid = gid;
+		new->sgid = new->fsgid = new->egid = gid;
 	}
 
 after_setid:
-- 
2.25.0