[PATCH] erofs: fix to avoid infinite loop in z_erofs_do_read_page() when read page beyond EOF

[PATCH] erofs: fix to avoid infinite loop in z_erofs_do_read_page() when read page beyond EOF

[Chunhai Guo]

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>
---
 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

Re: [PATCH] erofs: fix to avoid infinite loop in z_erofs_do_read_page() when read page beyond EOF

[Gao Xiang]

On 2023/7/10 17:34, Chunhai Guo wrote:
> 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>

I'd like to update the subject line manually to:

"erofs: avoid infinite loop in z_erofs_do_read_page() when reading beyond EOF"

since the original one is too long...

Otherwise it looks good to me,

Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang

Re: [PATCH] erofs: fix to avoid infinite loop in z_erofs_do_read_page() when read page beyond EOF

[Chao Yu]

On 2023/7/10 17:34, Chunhai Guo wrote:
> 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>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,