Messages in this thread Patch in this message | | | From | Maurizio Lombardi <> | Subject | [PATCH V3] mm: prevent page_frag_alloc() from corrupting the memory | Date | Fri, 15 Jul 2022 14:50:13 +0200 |
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A number of drivers call page_frag_alloc() with a fragment's size > PAGE_SIZE. In low memory conditions, __page_frag_cache_refill() may fail the order 3 cache allocation and fall back to order 0; In this case, the cache will be smaller than the fragment, causing memory corruptions.
Prevent this from happening by checking if the newly allocated cache is large enough for the fragment; if not, the allocation will fail and page_frag_alloc() will return NULL.
V2: do not free the cache page because this could make memory pressure even worse, just return NULL.
V3: add a comment to explain why we return NULL.
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com> --- mm/page_alloc.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e008a3df0485..59c4dddf379f 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5617,6 +5617,18 @@ void *page_frag_alloc_align(struct page_frag_cache *nc, /* reset page count bias and offset to start of new frag */ nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; offset = size - fragsz; + if (unlikely(offset < 0)) { + /* + * The caller is trying to allocate a fragment + * with fragsz > PAGE_SIZE but the cache isn't big + * enough to satisfy the request, this may + * happen in low memory conditions. + * We don't release the cache page because + * it could make memory pressure worse + * so we simply return NULL here. + */ + return NULL; + } } nc->pagecnt_bias--; -- 2.31.1
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