[PATCH 1/2] x86/crash: fix potential cmem->ranges array overflow

[Yuntao Wang]

The max_nr_ranges field of cmem allocated in crash_setup_memmap_entries()
is not initialized, its default value is 0.

When elfcorehdr is allocated from the middle of crashk_res due to any
potential reason, that is, `image->elf_load_addr > crashk_res.start &&
image->elf_load_addr + image->elf_headers_sz - 1 < crashk_res.end`,
executing memmap_exclude_ranges() will cause a range split to occur in
crash_exclude_mem_range(), which eventually leads to an overflow of the
cmem->ranges array.

Set cmem->max_nr_ranges to 1 to make crash_exclude_mem_range() return
-ENOMEM instead of causing cmem->ranges array overflow even when a split
happens.

Signed-off-by: Yuntao Wang <ytcoode@xxxxxxxxx>
---
 arch/x86/kernel/crash.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index c92d88680dbf..3be46f4b441e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -282,10 +282,6 @@ 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));
-	if (!cmem)
-		return -ENOMEM;
-
 	memset(&cmd, 0, sizeof(struct crash_memmap_data));
 	cmd.params = params;
 
@@ -321,6 +317,11 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 	}
 
 	/* Exclude some ranges from crashk_res and add rest to memmap */
+	cmem = vzalloc(struct_size(cmem, ranges, 1));
+	if (!cmem)
+		return -ENOMEM;
+	cmem->max_nr_ranges = 1;
+
 	ret = memmap_exclude_ranges(image, cmem, crashk_res.start, crashk_res.end);
 	if (ret)
 		goto out;
-- 
2.43.0