linux-kernel - [PATCH 4.4 82/93] aio: mark AIO pseudo-fs noexec

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Message-Id: <20161006074735.376922459@linuxfoundation.org>
Date:   Thu,  6 Oct 2016 10:29:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jann@...jh.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.4 82/93] aio: mark AIO pseudo-fs noexec

4.4-stable 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/aio.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -239,7 +239,12 @@ static struct dentry *aio_mount(struct f
 	static const struct dentry_operations ops = {
 		.d_dname	= simple_dname,
 	};
-	return mount_pseudo(fs_type, "aio:", NULL, &ops, AIO_RING_MAGIC);
+	struct dentry *root = mount_pseudo(fs_type, "aio:", NULL, &ops,
+					   AIO_RING_MAGIC);
+
+	if (!IS_ERR(root))
+		root->d_sb->s_iflags |= SB_I_NOEXEC;
+	return root;
 }
 
 /* aio_setup