aio: mark AIO pseudo-fs noexec

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>
[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@decadent.org.uk>

diff --git a/fs/aio.c b/fs/aio.c
index 7aaa4164bba59281d7f5541151c227cafba82acc..3e6d6974434c945084540ba0b730e53120c0a792 100644 (file)
--- 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))