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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Mike Galbraith <efault@gmx.de>,
        Borislav Petkov <bp@suse.de>, Dave Young <dyoung@redhat.com>
Subject: [PATCH 4.9 37/37] x86/crash: Fix crash_setup_memmap_entries() out-of-bounds access
Date:   Mon, 26 Apr 2021 09:29:38 +0200
Message-Id: <20210426072818.510231561@linuxfoundation.org>
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From: Mike Galbraith <efault@gmx.de>

commit 5849cdf8c120e3979c57d34be55b92d90a77a47e upstream.

Commit in Fixes: added support for kexec-ing a kernel on panic using a
new system call. As part of it, it does prepare a memory map for the new
kernel.

However, while doing so, it wrongly accesses memory it has not
allocated: it accesses the first element of the cmem->ranges[] array in
memmap_exclude_ranges() but it has not allocated the memory for it in
crash_setup_memmap_entries(). As KASAN reports:

  BUG: KASAN: vmalloc-out-of-bounds in crash_setup_memmap_entries+0x17e/0x3a0
  Write of size 8 at addr ffffc90000426008 by task kexec/1187

  (gdb) list *crash_setup_memmap_entries+0x17e
  0xffffffff8107cafe is in crash_setup_memmap_entries (arch/x86/kernel/crash.c:322).
  317                                      unsigned long long mend)
  318     {
  319             unsigned long start, end;
  320
  321             cmem->ranges[0].start = mstart;
  322             cmem->ranges[0].end = mend;
  323             cmem->nr_ranges = 1;
  324
  325             /* Exclude elf header region */
  326             start = image->arch.elf_load_addr;
  (gdb)

Make sure the ranges array becomes a single element allocated.

 [ bp: Write a proper commit message. ]

Fixes: dd5f726076cc ("kexec: support for kexec on panic using new system call")
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Young <dyoung@redhat.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/725fa3dc1da2737f0f6188a1a9701bead257ea9d.camel@gmx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/crash.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -23,6 +23,7 @@
 #include <linux/export.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
+#include <linux/overflow.h>
 
 #include <asm/processor.h>
 #include <asm/hardirq.h>
@@ -564,7 +565,7 @@ int crash_setup_memmap_entries(struct ki
 	struct crash_memmap_data cmd;
 	struct crash_mem *cmem;
 
-	cmem = vzalloc(sizeof(struct crash_mem));
+	cmem = vzalloc(struct_size(cmem, ranges, 1));
 	if (!cmem)
 		return -ENOMEM;