chmod: setuid/setgid bit bugfix and new tests.

* sysif.c (chmod_wrap): Again, related to the = operator, we
must not punch a hole in the suid and sgid bits for all
non-directory objects. This was based on a misinterpretation
of some coreutils documentation, and doesn't match the
actual behavior.  Rather, if the owner is a target (including
implicitly) then we mask out suid; and if the group owner is a
targe, then we mask out sgid.  Thus when we are doing a
permission set not targetting the owner we don't touch suid,
and similarly for the group owner and setgid.

* tests/018/chmod.tl: Failed test diagnostics now
identify which mode string was used.
Some existing tests involving the suid/sgid bits
have to be revised because this commit reflects
a correction in the requirements. One new test is added.

1 files changed, 2 insertions, 4 deletions

diff --git a/sysif.c b/sysif.c
index ee219ff3..44e236d7 100644
--- a/sysif.c
+++ b/sysif.c
@@ -643,14 +643,14 @@ static val chmod_wrap(val target, val mode)
             bits |= S_ISVTX;
 
           if (implicit_all || (who & CHM_U) != 0) {
-            mask |= 0700;
+            mask |= (0700 | S_ISUID);
             if ((srcm & 010))
               bits |= S_ISUID;
             bits |= (srcm & 7) << 6;
           }
 
           if (implicit_all || (who & CHM_G) != 0) {
-            mask |= 0070;
+            mask |= (0070 | S_ISGID);
             if ((srcm & 010))
               bits |= S_ISGID;
             bits |= (srcm & 7) << 3;
@@ -675,8 +675,6 @@ static val chmod_wrap(val target, val mode)
               cmode &= ~mask;
               if (implicit_all || (who & CHM_O) != 0)
                 cmode &= ~S_ISVTX; /* GNU Coreutils 8.28 chmod behavior */
-              if (!S_ISDIR(cmode))
-                cmode &= ~(S_ISUID | S_ISGID);
             }
             cmode |= bits;
             break;