[PATCH] kexec: avoid out of bounds in crash_exclude_mem_range()

[fuqiang wang]

When the split happened, judge whether mem->nr_ranges is equal to
mem->max_nr_ranges. If it is true, return -ENOMEM.

The advantage of doing this is that it can avoid array bounds caused by
some bugs. E.g., Before commit 4831be702b95 ("arm64/kexec: Fix missing
extra range for crashkres_low."), reserve both high and low memories for
the crashkernel may cause out of bounds.

On the other hand, move this code before the split to ensure that the
array will not be changed when return error.

Signed-off-by: fuqiang wang <fuqiang.wang@xxxxxxxxxxxx>
---
 kernel/crash_core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index efe87d501c8c..ffdc246cf425 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -611,6 +611,9 @@ int crash_exclude_mem_range(struct crash_mem *mem,
 		}
 
 		if (p_start > start && p_end < end) {
+			/* Split happened */
+			if (mem->nr_ranges == mem->max_nr_ranges)
+				return -ENOMEM;
 			/* Split original range */
 			mem->ranges[i].end = p_start - 1;
 			temp_range.start = p_end + 1;
@@ -626,9 +629,6 @@ int crash_exclude_mem_range(struct crash_mem *mem,
 	if (!temp_range.end)
 		return 0;
 
-	/* Split happened */
-	if (i == mem->max_nr_ranges - 1)
-		return -ENOMEM;
 
 	/* Location where new range should go */
 	j = i + 1;
-- 
2.42.0