From 0de59c27ebda76d3e5121888acca304e49009266 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Sun, 15 Nov 2015 23:13:16 -0500 Subject: [PATCH] runtime: handle sysReserve returning a pointer below the arena In mheap.sysAlloc, if an allocation at arena_used would exceed arena_end (but wouldn't yet push us past arena_start+_MaxArean32), it trie to extend the arena reservation by another 256 MB. It extends the arena by calling sysReserve, which, on 32-bit, calls mmap without MAP_FIXED, which means the address is just a hint and the kernel can put the mapping wherever it wants. In particular, mmap may choose an address below arena_start (the kernel also chose arena_start, so there could be lots of space below it). Currently, we don't detect this case and, if it happens, mheap.sysAlloc will corrupt arena_end and arena_used then return the low pointer to mheap.grow, which will crash when it attempts to index in to h_spans with an underflowed index. Fix this by checking not only that that p+p_size isn't too high, but that p isn't too low. Fixes #13143. Change-Id: I8d0f42bd1484460282a83c6f1a6f8f0df7fb2048 Reviewed-on: https://go-review.googlesource.com/16927 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Ian Lance Taylor --- src/runtime/malloc.go | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go index 8ce420a653..d9f52399b8 100644 --- a/src/runtime/malloc.go +++ b/src/runtime/malloc.go @@ -404,7 +404,7 @@ func (h *mheap) sysAlloc(n uintptr) unsafe.Pointer { if p == h.arena_end { h.arena_end = new_end h.arena_reserved = reserved - } else if p+p_size <= h.arena_start+_MaxArena32 { + } else if h.arena_start <= p && p+p_size <= h.arena_start+_MaxArena32 { // Keep everything page-aligned. // Our pages are bigger than hardware pages. h.arena_end = p + p_size