[PATCH 6.4 157/800] kexec: fix a memory leak in crash_shrink_memory()

Greg Kroah-Hartman
2023-07-16T20:00:08Z

From: Zhen Lei <thunder.leizhen@huawei.com>

[ Upstream commit 1cba6c4309f03de570202c46f03df3f73a0d4c82 ]

Patch series "kexec: enable kexec_crash_size to support two crash kernel
regions".

When crashkernel=X fails to reserve region under 4G, it will fall back to
reserve region above 4G and a region of the default size will also be
reserved under 4G. Unfortunately, /sys/kernel/kexec_crash_size only
supports one crash kernel region now, the user cannot sense the low memory
reserved by reading /sys/kernel/kexec_crash_size. Also, low memory cannot
be freed by writing this file.

For example:
resource_size(crashk_res) = 512M
resource_size(crashk_low_res) = 256M

The result of 'cat /sys/kernel/kexec_crash_size' is 512M, but it should be
768M. When we execute 'echo 0 > /sys/kernel/kexec_crash_size', the size
of crashk_res becomes 0 and resource_size(crashk_low_res) is still 256 MB,
which is incorrect.

Since crashk_res manages the memory with high address and crashk_low_res
manages the memory with low address, crashk_low_res is shrunken only when
all crashk_res is shrunken. And because when there is only one crash
kernel region, crashk_res is always used. Therefore, if all crashk_res is
shrunken and crashk_low_res still exists, swap them.

This patch (of 6):

If the value of parameter 'new_size' is in the semi-open and semi-closed
interval (crashk_res.end - KEXEC_CRASH_MEM_ALIGN + 1, crashk_res.end], the
calculation result of ram_res is:

ram_res->start = crashk_res.end + 1
ram_res->end = crashk_res.end

The operation of insert_resource() fails, and ram_res is not added to
iomem_resource. As a result, the memory of the control block ram_res is
leaked.

In fact, on all architectures, the start address and size of crashk_res
are already aligned by KEXEC_CRASH_MEM_ALIGN. Therefore, we do not need
to round up crashk_res.start again. Instead, we should round up
'new_size' in advance.

Link: https://lkml.kernel.org/r/20230527123439.772-1-thunder.leizhen@huawei.com
Link: https://lkml.kernel.org/r/20230527123439.772-2-thunder.leizhen@huawei.com
Fixes: 6480e5a09237 ("kdump: add missing RAM resource in crash_shrink_memory()")
Fixes: 06a7f711246b ("kexec: premit reduction of the reserved memory size")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Cong Wang <amwang@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/kexec_core.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 3d578c6fefee3..22acee18195a5 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1122,6 +1122,7 @@ int crash_shrink_memory(unsigned long new_size)
start = crashk_res.start;
end = crashk_res.end;
old_size = (end == 0) ? 0 : end - start + 1;
+ new_size = roundup(new_size, KEXEC_CRASH_MEM_ALIGN);
if (new_size >= old_size) {
ret = (new_size == old_size) ? 0 : -EINVAL;
goto unlock;
@@ -1133,9 +1134,7 @@ int crash_shrink_memory(unsigned long new_size)
goto unlock;
}

- start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
- end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);
-
+ end = start + new_size;
crash_free_reserved_phys_range(end, crashk_res.end);

if ((start == end) && (crashk_res.parent != NULL))
--
2.39.2