stdbuf cannot use libstdbuf on the same directory if /proc is masked

[oech3]

$ run0 mv /usr/lib/uutils-coreutils/libstdbuf.so -t /tmp
$ cp /usr/bin/stdbuf -t /tmp
$ unshare -rm bash -c "mount -t tmpfs tmpfs /proc && /tmp/stdbuf -oL true"
stdbuf: External libstdbuf not found at configured path: /usr/lib/uutils-coreutils/libstdbuf.so

$ unshare -rm bash -c "mount -t tmpfs tmpfs /proc && /tmp/gnu-stdbuf -oL true"
# success

I believe it is because std::env::current_exe() requires /proc/self/exe:

coreutils/src/uu/stdbuf/src/stdbuf.rs

Line 189 in e939eda

if let Ok(exe_path) = std::env::current_exe() {

[oech3]

@Ecordonnier

[oech3]

It seems GNU use argv[0]. But if we need to care about secutiry, we could use AT_EXECFN at least on Linux. I don't know what can we use for other platforms.

[Ecordonnier]

This is not security critical as far as I know, since stdbuf is not seteuid. I think the path discovery should be implemented the same way than in GNU coreutils.

[Ecordonnier]

What happens if those test steps are executed with GNU coreutils?

[oech3]

GNU tries to search libstdbuf based on argv[0] i.e. stdbuf success if libstdbuf.so is present at same dir with argv[0].

[oech3]

GNU found libstdbuf from PATH:

$ env PATH=/home/a/bin/gnu9.10 stdbuf -oL true # ok
$ mv '/home/a/bin/gnu9.10/libstdbuf.so' '/home/a/bin/gnu9.10/libstdbuf.so-'
$ env PATH=/home/a/bin/gnu9.10 stdbuf -oL true
stdbuf: failed to find `libstdbuf.so'

[oech3]

Since std rejected improving current_exe, I'll wait #10773 's uucore function.

[oech3]

I still have no idea how to do #11134 (comment) on non-Llinux.