Re: [PATCH] fchmodat, lchmod: port to buggy Linux filesystems

[Bruno Haible]

Paul Eggert wrote:
> > 2) Also the discussion what is the "right" behaviour is specific to Linux.
> > The code in the '#else' case
> > 
> >    if (S_ISLNK (st.st_mode))
> >      {
> >        close (fd);
> >        errno = EOPNOTSUPP;
> >        return -1;
> >      }
> > 
> > will surely upset users on BSD systems, where symlinks are intended to have
> > permission bits.
> 
> Because of the Autoconf tests, that code should be executed only on 
> platforms where lchmod fails (or does not exist), whould shouldn't occur 
> on BSD systems.

Unfortunately, it doesn't: The line in the module description

lib_SOURCES += lchmod.c

causes lchmod.c to be compiled (to a .o file that defines 'lchmod', not
even 'rpl_lchmod'!) on macOS, FreeBSD, NetBSD, etc.

> Still, I take your point that the code is confusing. 
> Perhaps lchmod.m4 and fchmodat.m4 should define a symbol 
> HAVE_LCHMOD_BUG_WITH_NON_SYMLINKS and the C code could refer to that. 
> The resulting machine code would be the same as now, but the 
> cause-and-effect would be clearer.

Yes, I agree. Let me do this. Also I'm adding more comments. This patch
is tested on all platforms that have an lchown() function.


Before:

                   HAVE_LCHMOD  REPLACE_LCHMOD   nm lchmod.o      nm fchmodat.o
glibc/Linux            0             0          rpl_fchmodat     
fchmodat,openat,chmod,...
macOS                  1             0          rpl_lstat,chmod  
save_cwd,chmod,lchmod,...
HP-UX                  1             0          rpl_lstat,chmod  
save_cwd,chmod,lchmod,...
musl/Linux             1             0          fchmodat         --
glibc/Hurd             1             0          fchmodat         --
glibc/kFreeBSD         1             0          fchmodat         --
FreeBSD                1             0          fchmodat         --
NetBSD                 1             0          fchmodat         --

After:

                   HAVE_LCHMOD  REPLACE_LCHMOD   nm lchmod.o      nm fchmodat.o
glibc/Linux            0             0          rpl_fchmodat     
fchmodat,openat,chmod,...
macOS                  1             0          --               
save_cwd,chmod,lchmod,...
HP-UX                  1             0          --               
save_cwd,chmod,lchmod,...
musl/Linux             1             0          --               --
glibc/Hurd             1             0          --               --
glibc/kFreeBSD         1             0          --               --
FreeBSD                1             0          --               --
NetBSD                 1             0          --               --


2020-02-16  Bruno Haible  <address@hidden>

        lchmod: Make more future-proof.
        * m4/lchmod.m4 (gl_FUNC_LCHMOD): Define NEED_LCHMOD_NONSYMLINK_FIX.
        (gl_PREREQ_LCHMOD): New macro.
        * lib/lchmod.c (orig_lchmod): New function.
        (lchmod): Test NEED_LCHMOD_NONSYMLINK_FIX. Access /proc only on Linux.
        Return EOPNOTSUPP only on Linux and on platforms without lchmod
        function.
        * modules/lchmod (configure.ac): Invoke gl_PREREQ_LCHMOD.

        lchmod: Fix buggy override on macOS, HP-UX (regression from 2020-02-08).
        * modules/lchmod (Makefile.am): Don't add lchmod.c to lib_SOURCES.

0001-lchmod-Fix-buggy-override-on-macOS-HP-UX-regression-.patch
Description: Text Data

0002-lchmod-Make-more-future-proof.patch
Description: Text Data