[Bug 1926246] Re: chrome based apps can not be run under qemu user mode

[Laurent Vivier]

I think this is the good approach to fix the problem, but exec_path can be not 
set in the case of
AT_EXECFD (binfmt_misc with credential flag) because we use execfd instead. You 
should use
do_openat() to get the file descriptor and execveat() to start the process.

Thanks,
Laurent

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https://bugs.launchpad.net/bugs/1926246

Title:
  chrome based apps can not be run under qemu user mode

Status in QEMU:
  New

Bug description:
  chrome uses /proc/self/exe to fork render process.
  Here a simple code to reproduce the issue. It's output parent then child but 
failed with qemu: unknown option 'type=renderer'.

  Maybe we can modify exec syscall to replace /proc/self/exe to the real
  path.

  //gcc -o self self.c 
  #include <stdio.h>
  #include <sys/types.h>
  #include <unistd.h>
  int main(int argc, char** argv) {
    if(argc==1){
      printf ("parent\n");
        if ( fork() == 0 )
      {
          return execl("/proc/self/exe","/proc/self/exe", 
"--type=renderer",NULL);
      }
    } else {
      printf ("child\n");
    }
    return 0;
  }

  similar reports:
  https://github.com/AppImage/AppImageKit/issues/965  
  https://github.com/golang/go/issues/42080  

  Workardound:
  compile chrome or your chrome based app with a patch to 
content/common/child_process_host_impl.cc:GetChildPath, get the realpath of 
/proc/self/exe:  

  diff --git a/content/common/child_process_host_impl.cc 
b/content/common/child_process_host_impl.cc
  index bc78aba80ac8..9fab74d3bae8 100644
  --- a/content/common/child_process_host_impl.cc
  +++ b/content/common/child_process_host_impl.cc
  @@ -60,8 +60,12 @@ base::FilePath ChildProcessHost::GetChildPath(int flags) {
   #if defined(OS_LINUX)
     // Use /proc/self/exe rather than our known binary path so updates
     // can't swap out the binary from underneath us.
  -  if (child_path.empty() && flags & CHILD_ALLOW_SELF)
  -    child_path = base::FilePath(base::kProcSelfExe);
  +  if (child_path.empty() && flags & CHILD_ALLOW_SELF) {
  +    if (!ReadSymbolicLink(base::FilePath(base::kProcSelfExe), &child_path)) {
  +      NOTREACHED() << "Unable to resolve " << base::kProcSelfExe << ".";
  +      child_path = base::FilePath(base::kProcSelfExe);
  +    }
  +  }
   #endif

     // On most platforms, the child executable is the same as the
  current

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