linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix uninit-value in f2fs

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Date:   Sat, 26 Sep 2020 07:31:19 +0800
From:   Chao Yu <chao@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     jaegeuk@...nel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix uninit-value in f2fs_lookup

On 2020-9-26 1:14, Eric Biggers wrote:
> On Fri, Sep 25, 2020 at 11:19:26PM +0800, Chao Yu wrote:
>> From: Chao Yu <yuchao0@...wei.com>
>>
>> As syzbot reported:
>>
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack+0x21c/0x280 lib/dump_stack.c:118
>>  kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:122
>>  __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:219
>>  f2fs_lookup+0xe05/0x1a80 fs/f2fs/namei.c:503
>>  lookup_open fs/namei.c:3082 [inline]
>>  open_last_lookups fs/namei.c:3177 [inline]
>>  path_openat+0x2729/0x6a90 fs/namei.c:3365
>>  do_filp_open+0x2b8/0x710 fs/namei.c:3395
>>  do_sys_openat2+0xa88/0x1140 fs/open.c:1168
>>  do_sys_open fs/open.c:1184 [inline]
>>  __do_compat_sys_openat fs/open.c:1242 [inline]
>>  __se_compat_sys_openat+0x2a4/0x310 fs/open.c:1240
>>  __ia32_compat_sys_openat+0x56/0x70 fs/open.c:1240
>>  do_syscall_32_irqs_on arch/x86/entry/common.c:80 [inline]
>>  __do_fast_syscall_32+0x129/0x180 arch/x86/entry/common.c:139
>>  do_fast_syscall_32+0x6a/0xc0 arch/x86/entry/common.c:162
>>  do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:205
>>  entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
>>
>> In f2fs_lookup(), @res_page could be used before being initialized,
>> because in __f2fs_find_entry(), once F2FS_I(dir)->i_current_depth was
>> been fuzzed to zero, then @res_page will never be initialized, causing
>> this kmsan warning, relocating @res_page initialization place to fix
>> this bug.
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>>  fs/f2fs/dir.c | 7 +++----
>>  1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
>> index 703cf8e21fc0..83630341ffa3 100644
>> --- a/fs/f2fs/dir.c
>> +++ b/fs/f2fs/dir.c
>> @@ -357,16 +357,15 @@ struct f2fs_dir_entry *__f2fs_find_entry(struct inode *dir,
>>  	unsigned int max_depth;
>>  	unsigned int level;
>>
>> +	*res_page = NULL;
>> +
>>  	if (f2fs_has_inline_dentry(dir)) {
>> -		*res_page = NULL;
>>  		de = f2fs_find_in_inline_dir(dir, fname, res_page);
>>  		goto out;
>>  	}
>>
>> -	if (npages == 0) {
>> -		*res_page = NULL;
>> +	if (npages == 0)
>>  		goto out;
>> -	}
>>
>>  	max_depth = F2FS_I(dir)->i_current_depth;
>>  	if (unlikely(max_depth > MAX_DIR_HASH_DEPTH)) {
>
> Can't the assignment to *res_page below be removed too?

Now I checked all branches in find_in_level(), it looks safe to remove *res_page
assignment in the loop.

Thanks,

>
>         for (level = 0; level < max_depth; level++) {
>                 *res_page = NULL;
>                 de = find_in_level(dir, level, fname, res_page);
>                 if (de || IS_ERR(*res_page))
>                         break;
>         }
>