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authorDomenico Cerasuolo <cerasuolodomenico@gmail.com>2023-09-22 19:22:11 +0200
committerAndrew Morton <akpm@linux-foundation.org>2023-09-29 17:20:47 -0700
commitca56489c2f1df516801eeff06129d2e9e282ab7b (patch)
treef0552b6e6a11e149523eb7340e40c60525f175e8
parent6f1bace9a9fb11402520ba7defa76bfaf7b8e09f (diff)
mm: zswap: fix potential memory corruption on duplicate store
While stress-testing zswap a memory corruption was happening when writing back pages. __frontswap_store used to check for duplicate entries before attempting to store a page in zswap, this was because if the store fails the old entry isn't removed from the tree. This change removes duplicate entries in zswap_store before the actual attempt. [cerasuolodomenico@gmail.com: add a warning and a comment, per Johannes] Link: https://lkml.kernel.org/r/20230925130002.1929369-1-cerasuolodomenico@gmail.com Link: https://lkml.kernel.org/r/20230922172211.1704917-1-cerasuolodomenico@gmail.com Fixes: 42c06a0e8ebe ("mm: kill frontswap") Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Nhat Pham <nphamcs@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Cc: Seth Jennings <sjenning@redhat.com> Cc: Vitaly Wool <vitaly.wool@konsulko.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r--mm/zswap.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/mm/zswap.c b/mm/zswap.c
index 412b1409a0d7..083c693602b8 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1219,6 +1219,19 @@ bool zswap_store(struct folio *folio)
return false;
/*
+ * If this is a duplicate, it must be removed before attempting to store
+ * it, otherwise, if the store fails the old page won't be removed from
+ * the tree, and it might be written back overriding the new data.
+ */
+ spin_lock(&tree->lock);
+ dupentry = zswap_rb_search(&tree->rbroot, offset);
+ if (dupentry) {
+ zswap_duplicate_entry++;
+ zswap_invalidate_entry(tree, dupentry);
+ }
+ spin_unlock(&tree->lock);
+
+ /*
* XXX: zswap reclaim does not work with cgroups yet. Without a
* cgroup-aware entry LRU, we will push out entries system-wide based on
* local cgroup limits.
@@ -1333,7 +1346,14 @@ insert_entry:
/* map */
spin_lock(&tree->lock);
+ /*
+ * A duplicate entry should have been removed at the beginning of this
+ * function. Since the swap entry should be pinned, if a duplicate is
+ * found again here it means that something went wrong in the swap
+ * cache.
+ */
while (zswap_rb_insert(&tree->rbroot, entry, &dupentry) == -EEXIST) {
+ WARN_ON(1);
zswap_duplicate_entry++;
zswap_invalidate_entry(tree, dupentry);
}