kernel: make sure fd is in range in fdclose()

as the Fgrp can be shared with other processes, we have to
recheck the fd index after locking the Fgrp in fdclose()
to make sure not to read beyond the bounds of the fd array.

1 files changed, 1 insertions, 1 deletions

diff --git a/sys/src/9/port/sysfile.c b/sys/src/9/port/sysfile.c
index 77ff43fa3..43d384c2e 100644
--- a/sys/src/9/port/sysfile.c
+++ b/sys/src/9/port/sysfile.c
@@ -294,7 +294,7 @@ fdclose(int fd, int flag)
 	Fgrp *f = up->fgrp;
 
 	lock(f);
-	c = f->fd[fd];
+	c = fd <= f->maxfd ? f->fd[fd] : nil;
 	if(c == nil || (flag != 0 && (c->flag&flag) == 0)){
 		unlock(f);
 		return;