erofs: fix out-of-bound access when z_erofs_gbuf_growsize() partially fails

If z_erofs_gbuf_growsize() partially fails on a global buffer due to
memory allocation failure or fault injection (as reported by syzbot [1]),
new pages need to be freed by comparing to the existing pages to avoid
memory leaks.

However, the old gbuf->pages[] array may not be large enough, which can
lead to null-ptr-deref or out-of-bound access.

Fix this by checking against gbuf->nrpages in advance.

[1] https://lore.kernel.org/r/000000000000f7b96e062018c6e3@google.com

Reported-by: syzbot+242ee56aaa9585553766@syzkaller.appspotmail.com
Fixes: d6db47e571dc ("erofs: do not use pagepool in z_erofs_gbuf_growsize()")
Cc: <stable@vger.kernel.org> # 6.10+
Reviewed-by: Chunhai Guo <guochunhai@vivo.com>
Reviewed-by: Sandeep Dhavale <dhavale@google.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240820085619.1375963-1-hsiangkao@linux.alibaba.com

diff --git a/fs/erofs/zutil.c b/fs/erofs/zutil.c
index 9b53883e5caf8acb5183b1d2e93cda3cf6b27fce..37afe202484091a90a90634e525954eb601b59e1 100644 (file)
--- a/fs/erofs/zutil.c
+++ b/fs/erofs/zutil.c
@@ -111,7 +111,8 @@ int z_erofs_gbuf_growsize(unsigned int nrpages)
 out:
        if (i < z_erofs_gbuf_count && tmp_pages) {
                for (j = 0; j < nrpages; ++j)
-                       if (tmp_pages[j] && tmp_pages[j] != gbuf->pages[j])
+                       if (tmp_pages[j] && (j >= gbuf->nrpages ||
+                                            tmp_pages[j] != gbuf->pages[j]))
                                __free_page(tmp_pages[j]);
                kfree(tmp_pages);
        }