Re: diffutils-3.10.242-d65b test failure on Slackware 14 and openSUSE 12.1

[Bruno Haible]

On Slackware 14 and openSUSE 12.1, there is a test failure:
FAIL: no-dereference

It can be easily reproduced like this:

  $ mkdir subdir
  $ ln -s loop loop
  $ ln -s loop subdir/loop
  $ diff --no-dereference loop subdir
  diff: subdir/loop: Bad file descriptor

Find also (attached) the system calls log of
  $ strace diff --no-dereference loop subdir

I debugged it:

diff.c:1442: oflags = 0xa0000
1st argument:
  diff.c:1484   openat (-100, "loop", 0xa0000) => fd = -1
  => fd = UNOPENED, err = 0
  diff.c:1526   fstatat (-100, "loop", ..., AT_SYMLINK_NOFOLLOW) => err = 0
2nd argument:
  diff.c:1484   openat (-100, "subdir", 0xa0000) => fd = 7
  diff.c:1528   fstat (7, ...) => err = 0
diff.c:1561
  fnm_arg = 0
  dir_arg = 1
  filename = "subdir/loop"
diff.c:1579   openat (7, "loop", O_RDONLY | 0xa0000) => -1, errno = ELOOP
diff.c:1583   openat (7, "loop", O_PATHSEARCH | 0xa0000) => 8

The last openat() call is the one that produces the "bad" file descriptor.

Find attached a program 'foo.c' that exhibits the interaction between
openat() and fstat() more directly. It fails on
  - Linux 3.1.0 (openSUSE 12.1)
  - Linux 3.2.29 (Slackware 14)

The manpage "man openat" explains it: O_PATH exists since Linux 2.6.39,
but is supported with fstat() only since Linux 3.6.

But the diff.c change from 2023-07-31 assumes that O_PATH is supported
with fstat() always.

The attached patch fixes the issue by using O_SEARCH instead of O_PATH
on these versions of Linux.

Bruno

slackware14-log
Description: Text document

foo.c
Description: Text Data

0001-diff-Fix-failure-of-no-dereference-option-regression.patch
Description: Text Data