Apply by doing:
       cd /usr/src
       patch -p0 < 025_getcwd.patch

And then rebuild and install libc:
       cd lib/libc
       make obj cleandir depend
       make && make install

Note that programs that are linked statically will not pick up the
change unless they are rebuilt.  To rebuild the static binaries
that use getcwd(3), run the following commands in the /usr/src/bin,
/usr/src/sbin and /usr/src/usr.bin/ftp directories:
       make obj cleandir depend
       make && make install

Index: lib/libc/gen/getcwd.c
===================================================================
RCS file: /cvs/src/lib/libc/gen/getcwd.c,v
retrieving revision 1.9
retrieving revision 1.10
diff -u -p -r1.9 -r1.10
--- lib/libc/gen/getcwd.c       11 Jun 2003 21:03:10 -0000      1.9
+++ lib/libc/gen/getcwd.c       5 Jan 2005 19:48:08 -0000       1.10
@@ -74,7 +74,7 @@ getcwd(char *pt, size_t size)
               }
               ept = pt + size;
       } else {
-               if ((pt = malloc(ptsize = 1024 - 4)) == NULL)
+               if ((pt = malloc(ptsize = MAXPATHLEN)) == NULL)
                       return (NULL);
               ept = pt + ptsize;
       }
@@ -82,13 +82,13 @@ getcwd(char *pt, size_t size)
       *bpt = '\0';

       /*
-        * Allocate bytes (1024 - malloc space) for the string of "../"'s.
+        * Allocate bytes for the string of "../"'s.
        * Should always be enough (it's 340 levels).  If it's not, allocate
        * as necessary.  Special * case the first stat, it's ".", not "..".
        */
-       if ((up = malloc(upsize = 1024 - 4)) == NULL)
+       if ((up = malloc(upsize = MAXPATHLEN)) == NULL)
               goto err;
-       eup = up + MAXPATHLEN;
+       eup = up + upsize;
       bup = up;
       up[0] = '.';
       up[1] = '\0';
@@ -133,8 +133,8 @@ getcwd(char *pt, size_t size)

                       if ((nup = realloc(up, upsize *= 2)) == NULL)
                               goto err;
+                       bup = nup + (bup - up);
                       up = nup;
-                       bup = up;
                       eup = up + upsize;
               }
               *bup++ = '.';
@@ -224,8 +224,7 @@ notfound:
err:
       if (ptsize)
               free(pt);
-       if (up)
-               free(up);
+       free(up);
       if (dir)
               (void)closedir(dir);
       return (NULL);