linux-kernel - [PATCH 3.16 18/19] aio: mark AIO pseudo-fs noexec

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Message-ID: <lsq.1491052670.668070856@decadent.org.uk>
Date:   Sat, 01 Apr 2017 14:17:50 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jann Horn" <jann@...jh.net>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 18/19] aio: mark AIO pseudo-fs noexec

3.16.43-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jann Horn <jann@...jh.net>

commit 22f6b4d34fcf039c63a94e7670e0da24f8575a5a upstream.

This ensures that do_mmap() won't implicitly make AIO memory mappings
executable if the READ_IMPLIES_EXEC personality flag is set.  Such
behavior is problematic because the security_mmap_file LSM hook doesn't
catch this case, potentially permitting an attacker to bypass a W^X
policy enforced by SELinux.

I have tested the patch on my machine.

To test the behavior, compile and run this:

    #define _GNU_SOURCE
    #include <unistd.h>
    #include <sys/personality.h>
    #include <linux/aio_abi.h>
    #include <err.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <sys/syscall.h>

    int main(void) {
        personality(READ_IMPLIES_EXEC);
        aio_context_t ctx = 0;
        if (syscall(__NR_io_setup, 1, &ctx))
            err(1, "io_setup");

        char cmd[1000];
        sprintf(cmd, "cat /proc/%d/maps | grep -F '/[aio]'",
            (int)getpid());
        system(cmd);
        return 0;
    }

In the output, "rw-s" is good, "rwxs" is bad.

Signed-off-by: Jann Horn <jann@...jh.net>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16: we don't have super_block::s_iflags; use
 file_system_type::fs_flags instead]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/aio.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -226,6 +226,7 @@ static int __init aio_setup(void)
 		.name		= "aio",
 		.mount		= aio_mount,
 		.kill_sb	= kill_anon_super,
+		.fs_flags	= FS_NOEXEC,
 	};
 	aio_mnt = kern_mount(&aio_fs);
 	if (IS_ERR(aio_mnt))