linux-kernel - [PATCH] erofs: fix to avoid infinite loop in z_erofs_do_read

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Date:   Mon, 10 Jul 2023 17:34:10 +0800
From:   Chunhai Guo <guochunhai@...o.com>
To:     xiang@...nel.org
Cc:     chao@...nel.org, huyue2@...lpad.com, jefflexu@...ux.alibaba.com,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Chunhai Guo <guochunhai@...o.com>
Subject: [PATCH] erofs: fix to avoid infinite loop in z_erofs_do_read_page() when read page beyond EOF

z_erofs_do_read_page() may loop infinitely due to the inappropriate
truncation in the below statement. Since the offset is 64 bits and min_t()
truncates the result to 32 bits. The solution is to replace unsigned int
with a 64-bit type, such as erofs_off_t.
    cur = end - min_t(unsigned int, offset + end - map->m_la, end);

    - For example:
        - offset = 0x400160000
        - end = 0x370
        - map->m_la = 0x160370
        - offset + end - map->m_la = 0x400000000
        - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
    - Expected result:
        - cur = 0
    - Actual result:
        - cur = 0x370

Signed-off-by: Chunhai Guo <guochunhai@...o.com>
---
 fs/erofs/zdata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index d9a0763f4595..b69d89a11dd0 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1035,7 +1035,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	 */
 	tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
 
-	cur = end - min_t(unsigned int, offset + end - map->m_la, end);
+	cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
 	if (!(map->m_flags & EROFS_MAP_MAPPED)) {
 		zero_user_segment(page, cur, end);
 		goto next_part;
-- 
2.25.1