mm: prevent page_frag_alloc() from corrupting the memory

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.

Link: https://lkml.kernel.org/r/20220715125013.247085-1-mlombard@redhat.com
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Cc: Chen Lin <chen45464546@163.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 19a0e4a23b2f1c36b322b9e8c913e60306c619c4..9d26c12f8e63a5a9c21673bc96ac27f51d43d2df 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5732,6 +5732,18 @@ refill:
                /* 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--;