Specify the size of s_volume_name in strscpy_pad() to avoid buffer
overflow.

Reported-by: syzbot+2cab87506a0e7885f4b9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2cab87506a0e7885f4b9
Signed-off-by: Pei Li <peili.dev@gmail.com>
---
strscpy_pad() by default takes the size of destination string as the
size to be read from source string. However, as s_volume_name is only
declared as an array of size EXT4_LABEL_MAX, we are reading 1 byte more
than expected.

Specify the size of s_volume_name in strscpy_pad() to avoid buffer
overflow.
---
 fs/ext4/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index dab7acd49709..0c4fb579757a 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1151,7 +1151,7 @@ static int ext4_ioctl_getlabel(struct ext4_sb_info *sbi, char __user *user_label
 	BUILD_BUG_ON(EXT4_LABEL_MAX >= FSLABEL_MAX);
 
 	lock_buffer(sbi->s_sbh);
-	strscpy_pad(label, sbi->s_es->s_volume_name);
+	strscpy_pad(label, sbi->s_es->s_volume_name, EXT4_LABEL_MAX);
 	unlock_buffer(sbi->s_sbh);
 
 	if (copy_to_user(user_label, label, sizeof(label)))

---
base-commit: 55027e689933ba2e64f3d245fb1ff185b3e7fc81
change-id: 20240628-bug8-7f700a228c4a

Best regards,
-- 
Pei Li <peili.dev@gmail.com>

On 2024/6/29 11:31, Pei Li wrote:
> Specify the size of s_volume_name in strscpy_pad() to avoid buffer
> overflow.
> 
> Reported-by: syzbot+2cab87506a0e7885f4b9@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2cab87506a0e7885f4b9

Please add,
Fixes: 744a56389f73 ("ext4: replace deprecated strncpy with alternatives")

> Signed-off-by: Pei Li <peili.dev@gmail.com>
> ---
> strscpy_pad() by default takes the size of destination string as the
> size to be read from source string. However, as s_volume_name is only
> declared as an array of size EXT4_LABEL_MAX, we are reading 1 byte more
> than expected.
> 

I'd suggested to move this into the commit log to make it easier to
understand, and IIUC this issue only happens when s_volume_name is full
of 16 bytes length since it's not NULL terminated, so it can't break out
after copying 16 bytes.

Thanks,
Yi.

> Specify the size of s_volume_name in strscpy_pad() to avoid buffer
> overflow.> ---
>  fs/ext4/ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index dab7acd49709..0c4fb579757a 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -1151,7 +1151,7 @@ static int ext4_ioctl_getlabel(struct ext4_sb_info *sbi, char __user *user_label
>  	BUILD_BUG_ON(EXT4_LABEL_MAX >= FSLABEL_MAX);
>  
>  	lock_buffer(sbi->s_sbh);
> -	strscpy_pad(label, sbi->s_es->s_volume_name);
> +	strscpy_pad(label, sbi->s_es->s_volume_name, EXT4_LABEL_MAX);
>  	unlock_buffer(sbi->s_sbh);
>  
>  	if (copy_to_user(user_label, label, sizeof(label)))
> 
> ---
> base-commit: 55027e689933ba2e64f3d245fb1ff185b3e7fc81
> change-id: 20240628-bug8-7f700a228c4a
> 
> Best regards,
>