linux-kernel - [PATCH 4.14 01/14] exec: Weaken dumpability for secureexec

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Date:   Thu,  4 Jan 2018 13:09:18 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tom Horsley <horsley1953@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.14 01/14] exec: Weaken dumpability for secureexec

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@...omium.org>

commit e816c201aed5232171f8eb80b5d46ae6516683b9 upstream.

This is a logical revert of commit e37fdb785a5f ("exec: Use secureexec
for setting dumpability")

This weakens dumpability back to checking only for uid/gid changes in
current (which is useless), but userspace depends on dumpability not
being tied to secureexec.

  https://bugzilla.redhat.com/show_bug.cgi?id=1528633

Reported-by: Tom Horsley <horsley1953@...il.com>
Fixes: e37fdb785a5f ("exec: Use secureexec for setting dumpability")
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/exec.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1350,9 +1350,14 @@ void setup_new_exec(struct linux_binprm
 
 	current->sas_ss_sp = current->sas_ss_size = 0;
 
-	/* Figure out dumpability. */
+	/*
+	 * Figure out dumpability. Note that this checking only of current
+	 * is wrong, but userspace depends on it. This should be testing
+	 * bprm->secureexec instead.
+	 */
 	if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP ||
-	    bprm->secureexec)
+	    !(uid_eq(current_euid(), current_uid()) &&
+	      gid_eq(current_egid(), current_gid())))
 		set_dumpable(current->mm, suid_dumpable);
 	else
 		set_dumpable(current->mm, SUID_DUMP_USER);