aio: mark AIO pseudo-fs noexec

BugLink: http://bugs.launchpad.net/bugs/1631468
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@thejh.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/fs/aio.c b/fs/aio.c
index 155f84253f331a4d9d13ffac3d1ea70322b09b11..fe4f49212b99ac5eb3e8692d07ab3315577ab246 100644 (file)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -239,7 +239,12 @@ static struct dentry *aio_mount(struct file_system_type *fs_type,
        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