The patch titled Subject: zsmalloc: don't underflow size calculation in zs_obj_write() has been added to the -mm mm-hotfixes-unstable branch. Its filename is zsmalloc-dont-underflow-size-calculation-in-zs_obj_write.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Sergey Senozhatsky senozhatsky@chromium.org Subject: zsmalloc: don't underflow size calculation in zs_obj_write() Date: Sun, 4 May 2025 20:00:22 +0900

Do not mix class->size and object size during offsets/sizes calculation in zs_obj_write(). Size classes can merge into clusters, based on objects-per-zspage and pages-per-zspage characteristics, so some size classes can store objects smaller than class->size. This becomes problematic when object size is much smaller than class->size - we can determine that object spans two physical pages, because we use a larger class->size for this, while the actual object is much smaller and fits one physical page, so there is nothing to write to the second page and memcpy() size calculation underflows.

We always know the exact size in bytes of the object that we are about to write (store), so use it instead of class->size.

Link: https://lkml.kernel.org/r/20250504110650.2783619-1-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org Reported-by: Igor Belousov igor.b@beldev.am Tested-by: Igor Belousov igor.b@beldev.am Cc: Minchan Kim minchan@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/zsmalloc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/mm/zsmalloc.c~zsmalloc-dont-underflow-size-calculation-in-zs_obj_write +++ a/mm/zsmalloc.c @@ -1243,19 +1243,19 @@ void zs_obj_write(struct zs_pool *pool, class = zspage_class(pool, zspage); off = offset_in_page(class->size * obj_idx);

- if (off + class->size <= PAGE_SIZE) { + if (!ZsHugePage(zspage)) + off += ZS_HANDLE_SIZE; + + if (off + mem_len <= PAGE_SIZE) { /* this object is contained entirely within a page */ void *dst = kmap_local_zpdesc(zpdesc);

- if (!ZsHugePage(zspage)) - off += ZS_HANDLE_SIZE; memcpy(dst + off, handle_mem, mem_len); kunmap_local(dst); } else { /* this object spans two pages */ size_t sizes[2];

- off += ZS_HANDLE_SIZE; sizes[0] = PAGE_SIZE - off; sizes[1] = mem_len - sizes[0];

_

Patches currently in -mm which might be from senozhatsky@chromium.org are

zsmalloc-dont-underflow-size-calculation-in-zs_obj_write.patch zsmalloc-prefer-the-the-original-pages-node-for-compressed-data-fix.patch zram-modernize-writeback-interface.patch zram-modernize-writeback-interface-v3.patch zram-modernize-writeback-interface-v4.patch zsmalloc-cleanup-headers-includes.patch documentation-zram-update-idle-pages-tracking-documentation.patch