linux-kernel - [PATCH] exec: Weaken dumpability for secureexec

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Date:   Tue, 2 Jan 2018 15:21:33 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Tom Horsley <horsley1953@...il.com>,
        Laura Abbott <labbott@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] exec: Weaken dumpability for secureexec

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")
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/exec.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 5688b5e1b937..7eb8d21bcab9 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1349,9 +1349,14 @@ void setup_new_exec(struct linux_binprm * bprm)
 
 	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);
-- 
2.7.4


-- 
Kees Cook
Pixel Security