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.
Reported-by: Igor Belousov igor.b@beldev.am Cc: stable@vger.kernel.org Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org --- mm/zsmalloc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 70406ac94bbd..999b513c7fdf 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1233,19 +1233,19 @@ void zs_obj_write(struct zs_pool *pool, unsigned long handle, 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];
On 2025-05-04 15:00, Sergey Senozhatsky wrote:
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.
Reported-by: Igor Belousov igor.b@beldev.am Cc: stable@vger.kernel.org Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org
Tested-by: Igor Belousov igor.b@beldev.am
mm/zsmalloc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 70406ac94bbd..999b513c7fdf 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1233,19 +1233,19 @@ void zs_obj_write(struct zs_pool *pool, unsigned long handle, 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];
On (25/05/04 20:00), Sergey Senozhatsky wrote:
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.
I think it's
Fixes: 44f76413496e ("zsmalloc: introduce new object mapping API")
On Sun, May 04, 2025 at 08:00:22PM +0900, Sergey Senozhatsky wrote:
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.
Reported-by: Igor Belousov igor.b@beldev.am Cc: stable@vger.kernel.org Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org
Could you please include user-visible effects and circumstances that Igor reported? Crash, backtrace etc, 16k pages etc. in the changelog?
This type of information helps tremendously with backports, or finding this patch when encountering the issue in the wild.
Acked-by: Johannes Weiner hannes@cmpxchg.org
On (25/05/06 09:56), Johannes Weiner wrote:
Could you please include user-visible effects and circumstances that Igor reported? Crash, backtrace etc, 16k pages etc. in the changelog?
This type of information helps tremendously with backports, or finding this patch when encountering the issue in the wild.
Fair enough. I'll send a v2 with updated commit message.
linux-stable-mirror@lists.linaro.org
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Igor Belousov -
Johannes Weiner -
Sergey Senozhatsky