[PATCH v2] erofs: Prevent entering an infinite loop when i is 0

[Gao Xiang]

On 2024/8/31 10:58, Gao Xiang wrote:
> Hi Sandeep,
> 
> On 2024/8/31 05:46, Sandeep Dhavale wrote:
>> Hi Liujinbao,
>> On Thu, Aug 29, 2024 at 5:24 AM liujinbao1 <jinbaoliu365 at gmail.com> wrote:
>>>
>>> From: liujinbao1 <liujinbao1 at xiaomi.com>
>>>
>>> When i=0 and err is not equal to 0,
>>> the while(-1) loop will enter into an
>>> infinite loop. This patch avoids this issue
>>>
>>> Signed-off-by: liujinbao1 <liujinbao1 at xiaomi.com>
>>> ---
>>>   fs/erofs/decompressor.c | 10 +++++-----
>>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
>>> index c2253b6a5416..672f097966fa 100644
>>> --- a/fs/erofs/decompressor.c
>>> +++ b/fs/erofs/decompressor.c
>>> @@ -534,18 +534,18 @@ int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb)
>>>
>>>   int __init z_erofs_init_decompressor(void)
>>>   {
>>> -       int i, err;
>>> +       int i, err = 0;
>>>
>>>          for (i = 0; i < Z_EROFS_COMPRESSION_MAX; ++i) {
>>>                  err = z_erofs_decomp[i] ? z_erofs_decomp[i]->init() : 0;
>>> -               if (err) {
>>> -                       while (--i)
>>> +               if (err && i) {
>>> +                       while (i--)
>> Actually there is a subtle bug in this fix. We will never enter the if
>> block here when i=0 and err is set which we were trying to fix.
>> This will cause z_erofs_decomp[0]->init() error to get masked and we
>> will continue the outer for loop (i.e. when i=0 and err is set).
> 

Ping? could anyone submit a proper fix for this?

Or just

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index c2253b6a5416..dfb77f4e68b4 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -539,8 +539,8 @@ int __init z_erofs_init_decompressor(void)
         for (i = 0; i < Z_EROFS_COMPRESSION_MAX; ++i) {
                 err = z_erofs_decomp[i] ? z_erofs_decomp[i]->init() : 0;
                 if (err) {
-                       while (--i)
-                               if (z_erofs_decomp[i])
+                       while (i)
+                               if (z_erofs_decomp[--i])
                                         z_erofs_decomp[i]->exit();
                         return err;
                 }

to avoid underflowed `i` (although it should have no real impact.)

Thanks,
Gao Xiang