[PATCH 6.10 002/149] erofs: fix out-of-bound access when z_erofs_gbuf_growsize() partially fails

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6.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

commit 0005e01e1e875c5e27130c5e2ed0189749d1e08a upstream.

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@xxxxxxxxxx

Reported-by: syzbot+242ee56aaa9585553766@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d6db47e571dc ("erofs: do not use pagepool in z_erofs_gbuf_growsize()")
Cc: <stable@xxxxxxxxxxxxxxx> # 6.10+
Reviewed-by: Chunhai Guo <guochunhai@xxxxxxxx>
Reviewed-by: Sandeep Dhavale <dhavale@xxxxxxxxxx>
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240820085619.1375963-1-hsiangkao@xxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/erofs/zutil.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/erofs/zutil.c
+++ b/fs/erofs/zutil.c
@@ -111,7 +111,8 @@ int z_erofs_gbuf_growsize(unsigned int n
 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);
 	}






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