linux(4): Use pwd_exec() to tell namei() about ABI root path

[dchagin]

Summary

PR: 72920

[freebsd_darkain.com]

This commit broke font rendering in desktop Linux apps.

They use /compat/linux/etc/fonts which is a symlink to /usr/local/etc/fonts

So something with this commit is preventing the following of symlinks when Linux apps are trying to open and read files.

Running the following command results in error

/compat/linux/usr/bin/fc-list
Fontconfig error: Cannot load default config file

[dchagin]

In D40090#921300, @freebsd_darkain.com wrote:

This commit broke font rendering in desktop Linux apps.

They use /compat/linux/etc/fonts which is a symlink to /usr/local/etc/fonts

So something with this commit is preventing the following of symlinks when Linux apps are trying to open and read files.

Running the following command results in error

/compat/linux/usr/bin/fc-list
Fontconfig error: Cannot load default config file

it would be nice to get ktrace/kdump output, some days ago Goran Mekic sent me a mail about an error related to this commit,
I reproduced the bug yesterday, here is a rather strange symptom of the problem, readlink("/proc/self/exe") succeed, however execve("/proc/self/exe") fails,
and it looks like recursive call inside namei()

[kib]

I think that in case of symbolic link with leading / in target, ISRESTARTED flag should be dropped, and lookup need to start from real root, instead of compat root. This should solve that sort of problems.

[dchagin]

In D40090#921300, @freebsd_darkain.com wrote:

This commit broke font rendering in desktop Linux apps.

They use /compat/linux/etc/fonts which is a symlink to /usr/local/etc/fonts

So something with this commit is preventing the following of symlinks when Linux apps are trying to open and read files.

Running the following command results in error

/compat/linux/usr/bin/fc-list
Fontconfig error: Cannot load default config file

https://reviews.freebsd.org/D40479