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ref: cb1b6c86fe82527f4c3c5f8f11ea4f5e4ae6a350
parent: 43e3393ad7bb57bef89fedfe2cd4f48c33588bcc
author: Roberto E. Vargas Caballero <k0ga@shike2.com>
date: Tue Oct 5 03:39:27 EDT 2021

libc: Avoid dangling pointers after fclose()

When a FILE is closed the pointers rp, rp and lp does
not make sense anymore, and they can point to a buffer
that is freed. Setting these pointers to NULL make
easier to detect wrong situations and return error in
those cases (for example in ungetc).

--- a/src/libc/stdio/fclose.c

+++ b/src/libc/stdio/fclose.c

@@ -22,7 +22,7 @@

 	if (fp->flags & _IOALLOC) {

 		free(fp->buf);

-		fp->buf = NULL;

+		fp->rp = fp->wp = fp->lp = fp->buf = NULL;

 	}

 	fp->flags &= ~(_IOWRITE | _IOREAD | _IORW |