[PATCH] exfat: check if cluster num is valid

[PATCH] exfat: check if cluster num is valid

[Tadeusz Struk]

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

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

Re: [PATCH] exfat: check if cluster num is valid

[Namjae Jeon]

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 ?

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
>
>

Re: [PATCH] exfat: check if cluster num is valid

[Namjae Jeon]

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
>>
>>
>

Re: [PATCH] exfat: check if cluster num is valid

[Tadeusz Struk]

Hi Jeon,
On 4/21/22 22:54, Namjae Jeon wrote:
>> 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 ?

Sorry, I missed this.
The reproducer [1] can be found on the syzbot report website [2]

[1] https://syzkaller.appspot.com/text?tag=ReproC&x=1353dfdf700000
[2] https://syzkaller.appspot.com/bug?id=50381fc73821ecae743b8cf24b4c9a04776f767c
-- 
Thanks,
Tadeusz

Re: [PATCH] exfat: check if cluster num is valid

[Tadeusz Struk]

On 4/29/22 20:26, Namjae Jeon wrote:
>> 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.

Ok, I will try a new version with is_valid_cluster()

-- 
Thanks,
Tadeusz