2021-01-25 18:12:55

by Casey Schaufler

Subject: Re: [PATCH] smackfs: restrict bytes count in smackfs write functions

On 1/24/2021 6:36 AM, Sabyrzhan Tasbolatov wrote:
> syzbot found WARNINGs in several smackfs write operations where
> bytes count is passed to memdup_user_nul which exceeds
> GFP MAX_ORDER. Check count size if bigger SMK_LONGLABEL,
> for smk_write_syslog if bigger than PAGE_SIZE - 1.
>
> Reported-by: [email protected]
> Signed-off-by: Sabyrzhan Tasbolatov <[email protected]>

Thank you for the patch. Unfortunately, SMK_LONGLABEL isn't
the right value in some of these cases.

> ---
> security/smack/smackfs.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
> index 5d44b7d258ef..88678c6f1b8c 100644
> --- a/security/smack/smackfs.c
> +++ b/security/smack/smackfs.c
> @@ -1167,7 +1167,7 @@ static ssize_t smk_write_net4addr(struct file *file, const char __user *buf,
> return -EPERM;
> if (*ppos != 0)
> return -EINVAL;
> - if (count < SMK_NETLBLADDRMIN)
> + if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
> return -EINVAL;
>
> data = memdup_user_nul(buf, count);
> @@ -1427,7 +1427,7 @@ static ssize_t smk_write_net6addr(struct file *file, const char __user *buf,
> return -EPERM;
> if (*ppos != 0)
> return -EINVAL;
> - if (count < SMK_NETLBLADDRMIN)
> + if (count < SMK_NETLBLADDRMIN || count > SMK_LONGLABEL)
> return -EINVAL;
>
> data = memdup_user_nul(buf, count);
> @@ -2647,6 +2647,8 @@ static ssize_t smk_write_syslog(struct file *file, const char __user *buf,
>
> if (!smack_privileged(CAP_MAC_ADMIN))
> return -EPERM;
> + if (count > PAGE_SIZE - 1)
> + return -EINVAL;
>
> data = memdup_user_nul(buf, count);
> if (IS_ERR(data))
> @@ -2744,6 +2746,8 @@ static ssize_t smk_write_relabel_self(struct file *file, const char __user *buf,
> */
> if (*ppos != 0)
> return -EINVAL;
> + if (count > SMK_LONGLABEL)
> + return -EINVAL;
>
> data = memdup_user_nul(buf, count);
> if (IS_ERR(data))

2021-01-25 22:47:19

by Tetsuo Handa

Subject: Re: [PATCH] smackfs: restrict bytes count in smackfs write functions

On 2021/01/26 3:08, Casey Schaufler wrote:
> On 1/24/2021 6:36 AM, Sabyrzhan Tasbolatov wrote:
>> syzbot found WARNINGs in several smackfs write operations where
>> bytes count is passed to memdup_user_nul which exceeds
>> GFP MAX_ORDER. Check count size if bigger SMK_LONGLABEL,
>> for smk_write_syslog if bigger than PAGE_SIZE - 1.
>>
>> Reported-by: [email protected]
>> Signed-off-by: Sabyrzhan Tasbolatov <[email protected]>
>
> Thank you for the patch. Unfortunately, SMK_LONGLABEL isn't
> the right value in some of these cases.
>

Since it uses sscanf(), I think that whitespaces must be excluded from upper limit
check. I'm proposing adding __GFP_NOWARM on the memdup_user_nul() side at
https://lkml.kernel.org/r/[email protected] .