[Samba] samba 4.12 build on hp-ux unsupported system calls

[Kumar, Arjit (SSTO)]

Hi Team,

>>  It's not possible to write a secure path-safe modern application without the XXXXat() calls.

Are you referring to secure path-safe applications due to below reasons mentioned in https://linux.die.net/man/2/openat. 

openat() and other similar system calls suffixed "at" are supported for two reasons.

First, openat() allows an application to avoid race conditions that could occur when using open(2) to open files in directories other than the current working directory. These race conditions result from the fact that some component of the directory prefix given to open(2) could be changed in parallel with the call to open(2). Such races can be avoided by opening a file descriptor for the target directory, and then specifying that file descriptor as the dirfd argument of openat().

Second, openat() allows the implementation of a per-thread "current working directory", via file descriptor(s) maintained by the application. (This functionality can also be obtained by tricks based on the use of /proc/self/fd/dirfd, but less efficiently.)

>> Either that or you'll have to add mappings in your libc to emulate these calls, but that won't be secure I'm afraid.

Earlier samba versions 4.11 and previous uses normal calls instead of *at() calls.
Is this change done to fix any specific security issue, which earlier version still have ?

If not then If we create wrappers and keep using older sys calls what type of issues may occur ?
  
Regards,
Arjit

-----Original Message-----
From: Jeremy Allison [mailto:jra at samba.org] 
Sent: Wednesday, April 8, 2020 9:41 PM
To: Kumar, Arjit (SSTO) <arjit.kumar at hpe.com>
Cc: samba at lists.samba.org
Subject: Re: [Samba] samba 4.12 build on hp-ux unsupported system calls

On Wed, Apr 08, 2020 at 09:58:26AM +0000, Kumar, Arjit (SSTO) via samba wrote:
> Hi Team,
> 
> We are having compile/linking time warning due unsatisfied system calls and macros.
> We have checked and confirm that these are not supported by hp-ux kernel and enabling them will require changes in VFS layer and physical filesystem.
> 
> Unsatisfied system calls
> 
> *        renameat
> 
> *        symlinkat
> 
> *        linkat
> 
> *        unlinkat
> 
> *        readlinkat
> 
> *        mkdirat
> 
> Undefined MACRO's
> 
> *        AT_REMOVEDIR
> 
> *        AT_FDCWD
> 
> These system calls have been added newly in samba 4.12.
> 
> Please provide workaround/patch to use older syscalls like mkdir,readlink,unlink etc within samba 4.12.

I'm afraid that can't be done.

It's not possible to write a secure path-safe modern application without the XXXXat() calls.

That's why we're moving to require them.

HPUX kernel will have to add these calls, or the HPUX ecosystem can't be maintained going forward. Sorry for the bad news :-(.

Either that or you'll have to add mappings in your libc to emulate these calls, but that won't be secure I'm afraid.