54567: zselect: don't pass fd>=FD_SETSIZE to FD_SET

zsh% zselect 2023
==2815== Syscall param select(exceptfds) points to uninitialised byte(s)
==2815==    at 0x4DDA2D6: select (in /lib64/libc-2.32.so)
==2815==    by 0x4885937: bin_zselect (zselect.c:175)
==2815==    by 0x410C5E: execbuiltin (builtin.c:506)
==2815==    by 0x43A5FC: execcmd_exec (exec.c:4259)
==2815==    by 0x433BE1: execpline2 (exec.c:2040)
==2815==    by 0x432824: execpline (exec.c:1765)
==2815==    by 0x431A7D: execlist (exec.c:1515)
==2815==    by 0x4310E3: execode (exec.c:1296)
==2815==    by 0x457D15: loop (init.c:223)
==2815==    by 0x45C151: zsh_main (init.c:1933)
==2815==    by 0x40FD61: main (main.c:93)
==2815==  Address 0x1ffeffe5b0 is on thread 1's stack
==2815==  in frame #1, created by bin_zselect (zselect.c:66)
zselect: error on select: bad file descriptor

1 files changed, 4 insertions, 0 deletions

diff --git a/Src/Modules/zselect.c b/Src/Modules/zselect.c
index 8c1267240..92a3b38c2 100644
--- a/Src/Modules/zselect.c
+++ b/Src/Modules/zselect.c
@@ -47,6 +47,10 @@ handle_digits(char *nam, char *argptr, fd_set *fdset, int *fdmax)
 	return 1;
     }
     fd = (int)zstrtol(argptr, &endptr, 10);
+    if (fd < 0 || fd >= FD_SETSIZE) {
+	zwarnnam(nam, "file descriptor out of range [0-%d]: %d", FD_SETSIZE-1, fd);
+	return 1;
+    }
     if (*endptr) {
 	zwarnnam(nam, "garbage after file descriptor: %s", endptr);
 	return 1;