From: Junrui Luo Date: Thu, 9 Apr 2026 13:59:39 +0000 (+0800) Subject: erofs: fix unsigned underflow in z_erofs_lz4_handle_overlap() X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=21e161de2dc660b1bb70ef5b156ab8e6e1cca3ab;p=thirdparty%2Fkernel%2Flinux.git erofs: fix unsigned underflow in z_erofs_lz4_handle_overlap() Some crafted images can have illegal (!partial_decoding && m_llen < m_plen) extents, and the LZ4 inplace decompression path can be wrongly hit, but it cannot handle (outpages < inpages) properly: "outpages - inpages" wraps to a large value and the subsequent rq->out[] access reads past the decompressed_pages array. However, such crafted cases can correctly result in a corruption report in the normal LZ4 non-inplace path. Let's add an additional check to fix this for backporting. Reproducible image (base64-encoded gzipped blob): H4sIAJGR12kCA+3SPUoDQRgG4MkmkkZk8QRbRFIIi9hbpEjrHQI5ghfwCN5BLCzTGtLbBI+g dilSJo1CnIm7GEXFxhT6PDDwfrs73/ywIQD/1ePD4r7Ou6ETsrq4mu7XcWfj++Pb58nJU/9i PNtbjhan04/9GtX4qVYc814WDqt6FaX5s+ZwXXeq52lndT6IuVvlblytLMvh4Gzwaf90nsvz 2DF/21+20T/ldgp5s1jXRaN4t/8izsy/OUB6e/Qa79r+JwAAAAAAAL52vQVuGQAAAP6+my1w ywAAAAAAAADwu14ATsEYtgBQAAA= $ mount -t erofs -o cache_strategy=disabled foo.erofs /mnt $ dd if=/mnt/data of=/dev/null bs=4096 count=1 Fixes: 598162d05080 ("erofs: support decompress big pcluster for lz4 backend") Reported-by: Yuhao Jiang Cc: stable@vger.kernel.org Signed-off-by: Junrui Luo Reviewed-by: Gao Xiang Signed-off-by: Gao Xiang --- diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c index 3c54e95964c9f..2b065f8c3f711 100644 --- a/fs/erofs/decompressor.c +++ b/fs/erofs/decompressor.c @@ -145,6 +145,7 @@ static void *z_erofs_lz4_handle_overlap(const struct z_erofs_decompress_req *rq, oend = rq->pageofs_out + rq->outputsize; omargin = PAGE_ALIGN(oend) - oend; if (!rq->partial_decoding && may_inplace && + rq->outpages >= rq->inpages && omargin >= LZ4_DECOMPRESS_INPLACE_MARGIN(rq->inputsize)) { for (i = 0; i < rq->inpages; ++i) if (rq->out[rq->outpages - rq->inpages + i] !=