Hi, Heiko

Thank you for the feedback.

Heiko Carstens hca@linux.ibm.com 于2025年10月27日周一 18:15写道：

On Sun, Oct 26, 2025 at 05:13:51PM +0800, Miaoqian Lin wrote:

...

When kvrealloc() fails, the original markers memory is leaked because the function directly assigns the NULL to the markers pointer, losing the reference to the original memory.

As a result, the kvfree() in pt_dump_init() ends up freeing NULL instead of the previously allocated memory.

Fix this by using a temporary variable to store kvrealloc()'s return value and only update the markers pointer on success.

Found via static anlaysis and this is similar to commit 42378a9ca553 ("bpf, verifier: Fix memory leak in array reallocation for stack state")

Fixes: d0e7915d2ad3 ("s390/mm/ptdump: Generate address marker array dynamically") Cc: stable@vger.kernel.org Signed-off-by: Miaoqian Lin linmq006@gmail.com

---

arch/s390/mm/dump_pagetables.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c index 9af2aae0a515..0f2e0c93a1e0 100644 --- a/arch/s390/mm/dump_pagetables.c +++ b/arch/s390/mm/dump_pagetables.c @@ -291,16 +291,19 @@ static int ptdump_cmp(const void *a, const void *b)

static int add_marker(unsigned long start, unsigned long end, const char *name) {

• struct addr_marker *new_markers;
  size_t oldsize, newsize;
  
  oldsize = markers_cnt * sizeof(*markers);
  newsize = oldsize + 2 * sizeof(*markers);
  if (!oldsize)
  

•         markers = kvmalloc(newsize, GFP_KERNEL);
  

•         new_markers = kvmalloc(newsize, GFP_KERNEL);
  else
  

•         markers = kvrealloc(markers, newsize, GFP_KERNEL);
  

• if (!markers)
  

•         new_markers = kvrealloc(markers, newsize, GFP_KERNEL);
  

• if (!new_markers)
          goto error;
  

• markers = new_markers;
  

This is not better to the situation before. If the allocation fails, markers_cnt will be set to zero, but the old valid markers pointer will stay, which means that the next call to add_marker() will allocate a new area via kvmalloc() instead of kvrealloc(), and thus leaking the old area too.

add_marker() needs to changes to return in a manner that both marker and marker_cnt correlate with each other. And I guess it is also easily possible to get rid of the two different allocation paths.

Care to send a new version?

I'm not sure if I can make it right. Do you think this way can fix the leak correctly? Thanks.

```diff static int add_marker(unsigned long start, unsigned long end, const char *name) { - size_t oldsize, newsize; - - oldsize = markers_cnt * sizeof(*markers); - newsize = oldsize + 2 * sizeof(*markers); - if (!oldsize) - markers = kvmalloc(newsize, GFP_KERNEL); - else - markers = kvrealloc(markers, newsize, GFP_KERNEL); - if (!markers) - goto error; + struct addr_marker *new_markers; + size_t newsize; + + newsize = (markers_cnt + 2) * sizeof(*markers); + new_markers = kvrealloc(markers, newsize, GFP_KERNEL); + if (!new_markers) + return -ENOMEM; + + markers = new_markers; markers[markers_cnt].is_start = 1; markers[markers_cnt].start_address = start; markers[markers_cnt].size = end - start; @@ -312,9 +311,6 @@ static int add_marker(unsigned long start, unsigned long end, const char *name) markers[markers_cnt].name = name; markers_cnt++; return 0; -error: - markers_cnt = 0; - return -ENOMEM; }