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From:   Namjae Jeon <linkinjeon@kernel.org>
Date:   Sat, 30 Apr 2022 12:26:56 +0900
Message-ID: <CAKYAXd8sQDJyftZ_N8bgCMcMCMraQ=6_8x+QZ5XprMN3P4x9gQ@mail.gmail.com>
Subject: Re: [PATCH] exfat: check if cluster num is valid
To:     Tadeusz Struk <tadeusz.struk@linaro.org>
Cc:     Sungjong Seo <sj1557.seo@samsung.com>,
        linux-fsdevel@vger.kernel.org, stable@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        syzbot+a4087e40b9c13aad7892@syzkaller.appspotmail.com
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2022-04-22 14:54 GMT+09:00, Namjae Jeon <linkinjeon@kernel.org>:
> 2022-04-19 2:39 GMT+09:00, Tadeusz Struk <tadeusz.struk@linaro.org>:
> Hi Tadeusz,
>
>> Syzbot reported slab-out-of-bounds read in exfat_clear_bitmap.
>> This was triggered by reproducer calling truncate with size 0,
>> which causes the following trace:
>>
>> BUG: KASAN: slab-out-of-bounds in exfat_clear_bitmap+0x147/0x490
>> fs/exfat/balloc.c:174
>> Read of size 8 at addr ffff888115aa9508 by task syz-executor251/365
>>
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack_lvl+0x1e2/0x24b lib/dump_stack.c:118
>>  print_address_description+0x81/0x3c0 mm/kasan/report.c:233
>>  __kasan_report mm/kasan/report.c:419 [inline]
>>  kasan_report+0x1a4/0x1f0 mm/kasan/report.c:436
>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
>>  exfat_clear_bitmap+0x147/0x490 fs/exfat/balloc.c:174
>>  exfat_free_cluster+0x25a/0x4a0 fs/exfat/fatent.c:181
>>  __exfat_truncate+0x99e/0xe00 fs/exfat/file.c:217
>>  exfat_truncate+0x11b/0x4f0 fs/exfat/file.c:243
>>  exfat_setattr+0xa03/0xd40 fs/exfat/file.c:339
>>  notify_change+0xb76/0xe10 fs/attr.c:336
>>  do_truncate+0x1ea/0x2d0 fs/open.c:65
> Could you please share how to reproduce this ?
Ping, If you apply this patch to your source, there is a problem. You
need to add +1 to EXFAT_DATA_CLUSTER_COUNT(sbi).
and please use is_valid_cluster() to check if cluster is valid instead of it.

>
> Thanks.
>>
>> Add checks to validate if cluster number is within valid range in
>> exfat_clear_bitmap() and exfat_set_bitmap()
>>
>> Cc: Namjae Jeon <linkinjeon@kernel.org>
>> Cc: Sungjong Seo <sj1557.seo@samsung.com>
>> Cc: linux-fsdevel@vger.kernel.org
>> Cc: stable@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>>
>> Link:
>> https://syzkaller.appspot.com/bug?id=50381fc73821ecae743b8cf24b4c9a04776f767c
>> Reported-by: syzbot+a4087e40b9c13aad7892@syzkaller.appspotmail.com
>> Fixes: 1e49a94cf707 ("exfat: add bitmap operations")
>> Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
>> ---
>>  fs/exfat/balloc.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
>> index 03f142307174..4ed81f86f993 100644
>> --- a/fs/exfat/balloc.c
>> +++ b/fs/exfat/balloc.c
>> @@ -149,6 +149,9 @@ int exfat_set_bitmap(struct inode *inode, unsigned
>> int
>> clu, bool sync)
>>  	struct exfat_sb_info *sbi = EXFAT_SB(sb);
>>
>>  	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
>> +	if (clu > EXFAT_DATA_CLUSTER_COUNT(sbi))
>> +		return -EINVAL;
>> +
>>  	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
>>  	i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
>>  	b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
>> @@ -167,6 +170,9 @@ void exfat_clear_bitmap(struct inode *inode, unsigned
>> int clu, bool sync)
>>  	struct exfat_mount_options *opts = &sbi->options;
>>
>>  	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
>> +	if (clu > EXFAT_DATA_CLUSTER_COUNT(sbi))
>> +		return;
>> +
>>  	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
>>  	i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
>>  	b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
>> --
>> 2.35.1
>>
>>
>