From a31ae8c508fc8d1bca4f57e9f9f88127572d5202 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Wed, 28 Apr 2021 04:03:49 +0200 Subject: [PATCH] [klibc] malloc: Fail if requested size > PTRDIFF_MAX malloc() adds some overhead to the requested size, which may result in an integer overflow and subsequent buffer overflow if it is close to SIZE_MAX. It should fail if size is large enough for this to happen. Further, it's not legal for a C object to be larger than PTRDIFF_MAX (half of SIZE_MAX) as pointer arithmetic within it could overflow. So return failure immediately if size is greater than that. CVE-2021-31873 Signed-off-by: Ben Hutchings --- usr/klibc/malloc.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/usr/klibc/malloc.c b/usr/klibc/malloc.c index bb57c9f6..abda84c2 100644 --- a/usr/klibc/malloc.c +++ b/usr/klibc/malloc.c @@ -147,6 +147,15 @@ void *malloc(size_t size) if (size == 0) return NULL; + /* Various additions below will overflow if size is close to + SIZE_MAX. Further, it's not legal for a C object to be + larger than PTRDIFF_MAX (half of SIZE_MAX) as pointer + arithmetic within it could overflow. */ + if (size > PTRDIFF_MAX) { + errno = ENOMEM; + return NULL; + } + /* Add the obligatory arena header, and round up */ size = (size + 2 * sizeof(struct arena_header) - 1) & ARENA_SIZE_MASK;