[PATCH v11 03/11] x86/kexec: Fix potential buffer overflow in prepare_elf_headers()

[Jinjie Ruan]

There is a race condition between the kexec_load() system call
(crash kernel loading path) and memory hotplug operations that can lead
to buffer overflow and potential kernel crash.

During prepare_elf_headers(), the following steps occur:
1. get_nr_ram_ranges_callback() queries current System RAM memory ranges
2. Allocates buffer based on queried count
3. prepare_elf64_ram_headers_callback() populates ranges from memblock

If memory hotplug occurs between step 1 and step 3, the number of ranges
can increase, causing out-of-bounds write when populating cmem->ranges[].

This happens because kexec_load() uses kexec_trylock (atomic_t) while
memory hotplug uses device_hotplug_lock (mutex), so they don't serialize
with each other.

Just add bounds checking in prepare_elf64_ram_headers_callback() to
prevent out-of-bounds (OOB) access,

Fixes: 8d5f894a3108 ("x86: kexec_file: lift CRASH_MAX_RANGES limit on crash_mem buffer")
Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 arch/x86/kernel/crash.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 335fd2ee9766..7fa6d45ebe3f 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -225,6 +225,9 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
 {
 	struct crash_mem *cmem = arg;
 
+	if (cmem->nr_ranges >= cmem->max_nr_ranges)
+		return -ENOMEM;
+
 	cmem->ranges[cmem->nr_ranges].start = res->start;
 	cmem->ranges[cmem->nr_ranges].end = res->end;
 	cmem->nr_ranges++;
-- 
2.34.1