add setxid.c for new set*id() framework. missed in last commit.

diff --git a/src/unistd/setxid.c b/src/unistd/setxid.c
new file mode 100644 (file)
index 0000000..d3bfaf6
--- /dev/null
+++ b/src/unistd/setxid.c
@@ -0,0 +1,49 @@
+#include <unistd.h>
+#include <errno.h>
+#include <sys/resource.h>
+#include "syscall.h"
+#include "libc.h"
+
+struct ctx {
+       int id, eid, sid;
+       int nr, rlim, err;
+};
+
+/* We jump through hoops to eliminate the possibility of partial failures. */
+
+static void do_setxid(void *p)
+{
+       struct ctx *c = p;
+       if (c->err) return;
+       if (c->rlim && c->id >= 0 && c->id != getuid()) {
+               struct rlimit inf = { RLIM_INFINITY, RLIM_INFINITY }, old;
+               getrlimit(RLIMIT_NPROC, &old);
+               if (setrlimit(RLIMIT_NPROC, &inf) && libc.threads_minus_1) {
+                       c->err = errno;
+                       return;
+               }
+               if (__syscall(c->nr, c->id, c->eid, c->sid))
+                       c->err = errno;
+               setrlimit(RLIMIT_NPROC, &old);
+               return;
+       }
+       if (__syscall(c->nr, c->id, c->eid, c->sid))
+               c->err = errno;
+}
+
+int __setxid(int nr, int id, int eid, int sid)
+{
+       struct ctx c = { .nr = nr, .id = id, .eid = eid, .sid = sid };
+       switch (nr) {
+       case SYS_setuid:
+       case SYS_setreuid:
+       case SYS_setresuid:
+               c.rlim = 1;
+       }
+       __synccall(do_setxid, &c);
+       if (c.err) {
+               errno = c.err;
+               return -1;
+       }
+       return 0;
+}