[PATCH v15 14/23] LoongArch: kexec_file: Fix TOCTOU buffer overflow via memory region padding

[Jinjie Ruan]

Sashiko AI code review pointed out there is a TOCTOU (Time-of-Check to
Time-of-Use) race condition in prepare_elf_headers() between the initial
pass that counts System RAM ranges and the second pass that populates them.
If a memory hotplug event occurs between these two steps, the number of
memory regions may increase, causing an out-of-bounds write to
the cmem->ranges[] array.

Fix this fundamentally by using `CRASH_HOTPLUG_SAFETY_PADDING` (128 slots)
to expand the flexible array allocation ceiling upfront. This safely
absorbs any concurrent memory region expansion. Concurrently, add
a defensive boundary check to return -EAGAIN on unexpected overrun,
fully eradicating the overflow window and ensuring system stability.

Cc: Youling Tang <tangyouling@xxxxxxxxxx>
Cc: Huacai Chen <chenhuacai@xxxxxxxxxxx>
Cc: WANG Xuerui <kernel@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 1bcca8620a91 ("LoongArch: Add crash dump support for kexec_file")
Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
 arch/loongarch/kernel/machine_kexec_file.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/kernel/machine_kexec_file.c b/arch/loongarch/kernel/machine_kexec_file.c
index 5584b798ba46..3c369124586e 100644
--- a/arch/loongarch/kernel/machine_kexec_file.c
+++ b/arch/loongarch/kernel/machine_kexec_file.c
@@ -64,7 +64,8 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	phys_addr_t start, end;
 	struct crash_mem *cmem;
 
-	nr_ranges = 2; /* for exclusion of crashkernel region */
+	/* for exclusion of crashkernel region */
+	nr_ranges = 2 + CRASH_HOTPLUG_SAFETY_PADDING;
 	for_each_mem_range(i, &start, &end)
 		nr_ranges++;
 
@@ -75,6 +76,11 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	cmem->max_nr_ranges = nr_ranges;
 	cmem->nr_ranges = 0;
 	for_each_mem_range(i, &start, &end) {
+		if (unlikely(cmem->nr_ranges >= cmem->max_nr_ranges)) {
+			ret = -EAGAIN;
+			goto out;
+		}
+
 		cmem->ranges[cmem->nr_ranges].start = start;
 		cmem->ranges[cmem->nr_ranges].end = end - 1;
 		cmem->nr_ranges++;
-- 
2.34.1