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.

2 files changed, 8 insertions, 9 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;
diff --git a/tests/018/chmod.tl b/tests/018/chmod.tl
index 16b96ad0..f815548c 100644
--- a/tests/018/chmod.tl
+++ b/tests/018/chmod.tl
@@ -19,8 +19,8 @@
     (let* ((st (stat tgt))
            (m (logand st.mode #xFFF)))
       (unless (eql m exp)
-        (error "failed to set mode: expected ~s, actual ~s"
-               expected (enc-perm m))))))
+        (error "failed to set mode with ~s: expected ~s, actual ~s"
+               mode expected (enc-perm m))))))
 
 (remove-path tgt)
 (with-stream (s (open-file tgt "w")))
@@ -32,10 +32,11 @@
 (cht "------------" "g+s"               "-g----------")
 (cht "------------" "+t"                "--t---------")
 (cht "sgtrwxrwxrwx" "="                 "------------")
-(cht "sgtrwxrwxrwx" "u="                "--t---rwxrwx")
-(cht "sgtrwxrwxrwx" "g="                "--trwx---rwx")
-(cht "sgtrwxrwxrwx" "o="                "---rwxrwx---")
+(cht "sgtrwxrwxrwx" "u="                "-gt---rwxrwx")
+(cht "sgtrwxrwxrwx" "g="                "s-trwx---rwx")
+(cht "sgtrwxrwxrwx" "o="                "sg-rwxrwx---")
 (cht "------------" "u+s,g+s"           "sg----------")
 (cht "------------" "u+r,g+r,o+r,+t,+s" "sgtr--r--r--")
 (cht "------------" "+rwx,g-r+w,o-r+w"  "---rwx-wx-wx")
 (cht "---------rwx" "u=rwsx"            "s--rwx---rwx")
+(cht "---------rwx" "u=rwsx,g=rwx,go-x" "s--rwxrw-rw-")