From 6d1a3dfeaf2caac4033a3c65822fb4e7e14866c7 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 28 Mar 2016 23:41:17 -0400 Subject: fix undefined pointer comparison in stdio-internal __toread the comparison f->wpos > f->buf has undefined behavior when f->wpos is a null pointer, despite the intuition (and actual compiler behavior, for all known compilers) being that NULL > ptr is false for all valid pointers ptr. the purpose of the comparison is to determine if the write buffer is non-empty, and the idiom used elsewhere for that is comparison against f->wbase, which is either a null pointer when not writing, or equal to f->buf when writing. in the former case, both f->wpos and f->wbase are null; in the latter they are both non-null and point into the same array. --- src/stdio/__toread.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/stdio/__toread.c b/src/stdio/__toread.c index b08f5bb4..35f67b8f 100644 --- a/src/stdio/__toread.c +++ b/src/stdio/__toread.c @@ -3,7 +3,7 @@ int __toread(FILE *f) { f->mode |= f->mode-1; - if (f->wpos > f->buf) f->write(f, 0, 0); + if (f->wpos > f->wbase) f->write(f, 0, 0); f->wpos = f->wbase = f->wend = 0; if (f->flags & F_NORD) { f->flags |= F_ERR; -- cgit v1.2.1