Here is a simple dockerfile to cross build:

FROM debian:buster

ENV DEBIAN_FRONTEND=noninteractive

RUN useradd -u 501 -ms /bin/bash build
RUN apt-get clean && apt-get update
RUN apt-get install -y 
    git 
    sudo 
    sed 
    wget 
    cpio 
    unzip 
    rsync 
    bc 
    bison 
    flex 
    libssl-dev 
    make 
    kmod 
    libc6-dev 
    libncurses5-dev 
    crossbuild-essential-armhf 
    crossbuild-essential-arm64

WORKDIR /home/build
USER build
VOLUME ["/home/build"]

and script I’m running:

# Defaults
IMAGE_NAME=${IMAGE_NAME:-"linux_builder"}
ARCH=${ARCH:-"arm"}
CORES=${CORES:-0}
KERNEL=${KERNEL:-"kernel7"}
CROSS_COMPILE=${CROSS_COMPILE:-"arm-linux-gnueabihf-"}
VOLUME="$(pwd)/fs"

# Run builder environment
podman run --rm 
    --device /dev/fuse 
    --cap-add SYS_ADMIN 
    --name $IMAGE_NAME 
    -v $VOLUME:"/home/build/fs" 
    -e ARCH=$ARCH 
    -e KERNEL=$KERNEL 
    -e CROSS_COMPILE=$CROSS_COMPILE 
    -it 
    $IMAGE_NAME 
    bash $@

When I checkout buildroot into home directory it compiles withour any problem.
But if I use mounted directory instead I get weird error:

  /bin/bash ./libtool   --mode=install /usr/bin/install -c pkgconf '/home/build/buildroot/output/host/bin'
libtool: install: /usr/bin/install -c pkgconf /home/build/buildroot/output/host/bin/pkgconf
make[2]: Leaving directory '/home/build/fs/buildroot/output/build/host-pkgconf-1.6.3'
make[1]: Leaving directory '/home/build/fs/buildroot/output/build/host-pkgconf-1.6.3'
/usr/bin/install -m 0755 -D package/pkgconf/pkg-config.in /home/build/fs/buildroot/output/host/bin/pkg-config
/bin/sed -i -e 's,@STAGING_SUBDIR@,arm-buildroot-linux-gnueabihf/sysroot,g' /home/build/fs/buildroot/output/host/bin/pkg-config
/bin/sed: couldn't open temporary file /home/build/fs/buildroot/output/host/bin/sedWes6rs: Permission denied
make: *** [package/pkg-generic.mk:300: /home/build/fs/buildroot/output/build/host-pkgconf-1.6.3/.stamp_host_installed] Error 4

The same problem is when running as root.

Any idea what is going on?

Thanks for help!