failed to open /usr/lib/x86_64-linux-gnu/libc.so.6 when injecting

[BrandowLucas]

shell ~ sudo ./injector -n procExample -p 2167 ~/lib.so

targeting process "procExample" with pid 2167
targeting process with pid 2167

failed to open /usr/lib/x86_64-linux-gnu/libc.so.6. (dev:0x1b, ino:557139)

I was getting this error on Arch Linux, now I tried on Ubuntu 22 LTS and I could reproduce the same issue.

Until some months ago I could inject this same shared library on the same process id, now I can't anymore.

ldd --version
ldd (Ubuntu GLIBC 2.35-0ubuntu3.8) 2.35 / 2.39 (on arch-linux)

[Brandon-T]

static inline int is_on_overlay_fs(int fd)
{
    struct statfs sbuf;
    if (fstatfs(fd, &sbuf) != 0) {
        DEBUG(" fstatfs() error %s\n", strerror(errno));
        return -1;
    }
#ifndef OVERLAYFS_SUPER_MAGIC
#define OVERLAYFS_SUPER_MAGIC 0x794c7630
#endif
    return (sbuf.f_type == OVERLAYFS_SUPER_MAGIC) ? 1 : 0;
}

This line is causing the issue. On Fedora Workstation for example, sbuf.f_type is BTRFS_SUPER_MAGIC and not OVERLAYFS_SUPER_MAGIC. If I comment out that line and return true (1), it works just fine. So this check will break on different file system types.

There are a ton of Linux file-systems that this library works on, but will fail due to the above check. https://man7.org/linux/man-pages/man2/statfs.2.html lists all of them.

cc: @kubo . It might be better to try the injection, and if it fails, then return an error, rather than trying to detect all the file-system types.