erofs: avoid infinite loop in z_erofs_do_read_page() when reading 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@vivo.com>
Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230710093410.44071-1-guochunhai@vivo.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index d9a0763..b69d89a 100644 (file)
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1035,7 +1035,7 @@ hitted:
         */
        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;