Subject: bug#70214: 'install' fails to copy regular file to autofs/cifs, due to ACL or xattr handling

From: Andreas Grünbacher <[email-masked]>
Date: Mon, 15 Apr 2024 16:37:25 +0200

Hello,

Am So., 14. Apr. 2024 um 00:43 Uhr schrieb Pádraig Brady <[email-masked]>:
> On 13/04/2024 20:29, Bruno Haible wrote:
> > Hi Pádraig,
> >
> > I wrote:
> >>> 5) The same thing with 'cp -a' succeeds:
> >>>
> >>> $ build-sparc64/src/cp -a /var/tmp/foo3941 $HOME/foo3941; echo $?
> >>> 0
> >>> $ build-sparc64-no-acl/src/cp -a /var/tmp/foo3941 $HOME/foo3941; echo $?
> >>> 0
> >
> > You wrote:
> >> The psuedo code that install(1) uses is:
> >>
> >> copy_reg()
> >>     if (x->set_mode) /* install */
> >>       set_acl(dest, x->mode /* 600 */)
> >>         ctx->acl = acl_from_mode ( /* 600 */)
> >>         acl_set_fd (ctx->acl) /* fails EACCES */
> >>         if (! acls_set)
> >>            must_chmod = true;
> >>         if (must_chmod)
> >>           saved_errno = EACCES;
> >>           chmod (ctx->mode /* 600 */)
> >>           if (save_errno)
> >>             return -1;
> >
> > And, for comparison, what is the pseudo-code that 'cp -a' uses?
> > I would guess that there must be a relevant difference between both.
>
> The cp pseudo code is:
>
> copy_reg()
>    if (preserve_xattr)
>      copy_attr()
>        ret = attr_copy_fd()
>        if (ret == -1 && require_preserve_xattr /*false*/)
>          return failure;
>    if (preserve_mode)
>      copy_acl()
>        qcopy_acl()
>          #if USE_XATTR /* true */
>            fchmod() /* chmod before setting ACLs as doing after may reset */
>            return attr_copy_fd() /* successful if no ACLs in source */
>          #endif
>
> If however you add ACLs in the source, you induce a similar failure:
>
> $ setfacl -m u:nobody:r /var/tmp/foo3942
> $ src/cp -a /var/tmp/foo3942 foo3942; echo $?
> src/cp: preserving permissions for ‘foo3942’: Permission denied
> 1
>
> The corresponding strace is:
>
> fchmod(4, 0100640)                      = 0
> flistxattr(3, NULL, 0)                  = 24
> flistxattr(3, "system.posix_acl_access\0", 24) = 24
> fgetxattr(3, "system.posix_acl_access", NULL, 0) = 44
> fgetxattr(3, "system.posix_acl_access", "\2\0...\4", 44) = 44
> fsetxattr(4, "system.posix_acl_access", "\2\0...\4", 44, 0) = -1 EACCES (Permission denied)

Why does CIFS think EACCES is an appropriate error to return here? The
fchmod() succeeds, so changing the file permissions via fsetxattr()
should really succeed as well.

Thanks,
Andreas