Re: fatal: Could not get current working directory: Permission denied | affected 2.10,2.11,2.12, but not 1.9.5 |

Od: "René Scharfe" <l.s.r@web.de>
Do: "Stefan Beller" <sbeller@google.com>; 
Wysłane: 22:08 Piątek 2017-03-17
Temat: Re: fatal: Could not get current working directory: Permission denied | affected 2.10,2.11,2.12, but not 1.9.5 |

quoted

Am 17.03.2017 um 20:45 schrieb Stefan Beller:
On Fri, Mar 17, 2017 at 12:34 PM, René Scharfe  wrote:

quoted

Am 15.03.2017 um 22:30 schrieb René Scharfe:

quoted

Am 15.03.2017 um 10:44 schrieb Zenobiusz Kunegunda:

quoted

$ git bisect bad
7333ed1788b4f2b162a35003044d77a716732a1f is the first bad commit
commit 7333ed1788b4f2b162a35003044d77a716732a1f
Author: René Scharfe 
Date:   Mon Jul 28 20:26:40 2014 +0200

    setup: convert setup_git_directory_gently_1 et al. to strbuf

That's what I half-suspected, and I think by now I got an idea.  Here's
a test program:

And here's a patch for letting strbuf_getcwd() use the same getcwd(3)
extension that pwd(1) uses.  It avoids the need to guess the path's
length and thus reduces the chance of stumbling over strange error
codes.  I wonder if it helps in your case.

René

---
 strbuf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/strbuf.c b/strbuf.c
index ace58e7367..4c02801edd 100644
--- a/strbuf.c
+++ b/strbuf.c

@@ -442,6 +442,14 @@ int strbuf_getcwd(struct strbuf *sb)
 {
        size_t oldalloc = sb->alloc;
        size_t guessed_len = 128;
+       char *cwd;
+
+       cwd = getcwd(NULL, 0);

from my local man pages:

  As  an extension to the POSIX.1-2001 standard, Linux (libc4, libc5,
glibc) getcwd()
  allocates the buffer dynamically using malloc(3) if buf is NULL.  In
this case, the
  allocated buffer has the length size unless size is zero, when buf
is allocated as big
  as necessary.  The caller should free(3) the returned buffer.

This sounds specific to Linux (though I am reading Linux man pages,
which claim this; Also it seems I might have misread it as it also states
"The pathname is returned as the function result and via the
argument buf, if present.").

I'm only interested in FreeBSD for now, as that's the platform Zenobiusz 
reported the issue on and I haven't been able to reproduce it, so this 
is still a bit exploratory, but hopefully getting closer.  This 
extension is used in the first version of pwd(1) in FreeBSD's repo, 
comitted 1994-05-26, so it was supported there basically forever.

The oldest version I found that's using the extention is NetBSD's 
pwd(1), which was committed 1993-03-21 and carries a SCCS timestamp of 
1991-02-20.  Visual Studio .NET 2003 supports it as well.

quoted

Looking further:

  These functions are often used to save the location of the current
  working directory for the purpose of returning to it later.  Opening the
  current directory (".")  and  calling  fchdir(2)  to return is
usually a faster
  and more reliable alternative when sufficiently many file descriptors are
  available, especially on platforms other than Linux.

Not sure if that opens another door here?

Reducing the use of absolute paths may be a good idea in general, but 
that would probably require major changes.  And Windows doesn't seem to 
offer fchdir() at all; I don't know if it has an equivalent function 
that could be used to build a replacement.

René

I think I found a way to reproduce this error.
I installed FreeBSD 10.3 under qemu with zfs partitioning.
Test program did not report any access errors.
Then I did chmod 711 /usr/home
Now program started reporting permission denied errors just like this:
   $ ./a.out  
   len = 0, errno = 22, Invalid argument
   len = 1, errno = 34, Result too large
   len = 2, errno = 13, Permission denied
   len = 20, errno = 0, No error: 0