[PATCH v2 1/2] x86/kexec: Fix potential out of bounds in crash_setup_memmap_entries()

[fuqiang wang]

In memmap_exclude_ranges(), there will exclude elfheader from
crashk_res. In the current x86 architecture code, the elfheader is
always allocated at crashk_res.start. It seems that there won't be a
split a new range. But it depends on the allocation position of
elfheader in crashk_res. To avoid potential out of bounds in future, Set
the array size to 2.

But similar issue will not exist in fill_up_crash_elf_data(). Because
the range to be excluded is [0, 1M], start (0) is special and will not
appear in the middle of existing cmem->ranges[]. I added a comment to
explain it.

Signed-off-by: fuqiang wang <fuqiang.wang at easystack.cn>
---
 arch/x86/kernel/crash.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c92d88680dbf..1c15d0884c90 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -149,6 +149,13 @@ static struct crash_mem *fill_up_crash_elf_data(void)
 	/*
 	 * Exclusion of crash region and/or crashk_low_res may cause
 	 * another range split. So add extra two slots here.
+	 *
+	 * Exclusion of low 1M may not cause another range split, because the
+	 * range of exclude is [0, 1M] and the condition for splitting a new
+	 * region is that the start, end parameters are both in a certain
+	 * existing region in cmem and cannot be equal to existing region's
+	 * start or end. Obviously, the start of [0, 1M] cannot meet this
+	 * condition.
 	 */
 	nr_ranges += 2;
 	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
@@ -282,9 +289,15 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 	struct crash_memmap_data cmd;
 	struct crash_mem *cmem;
 
-	cmem = vzalloc(struct_size(cmem, ranges, 1));
+	cmem = vzalloc(struct_size(cmem, ranges, 2));
 	if (!cmem)
 		return -ENOMEM;
+	cmem->max_nr_ranges = 2;
+
+	/* Exclude some ranges from crashk_res and add rest to memmap */
+	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
+	if (ret)
+		goto out;
 
 	memset(&cmd, 0, sizeof(struct crash_memmap_data));
 	cmd.params = params;
@@ -320,11 +333,6 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 		add_e820_entry(params, &ei);
 	}
 
-	/* Exclude some ranges from crashk_res and add rest to memmap */
-	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
-	if (ret)
-		goto out;
-
 	for (i = 0; i < cmem->nr_ranges; i++) {
 		ei.size = cmem->ranges[i].end - cmem->ranges[i].start + 1;
 
-- 
2.42.0