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SubjectRe: [PATCH 1/3] extend get/setrlimit to support setting rlimits external to a process (v3)
Neil Horman wrote:
>>> +static ssize_t proc_pid_limit_write(struct file *file, const char __user *buf,
>>> + size_t count, loff_t *ppos)
>>> +{
>>> + char *buffer;
>>> + char *element, *vmc, *vmm;
>>> + struct rlimit new_rlim;
>>> + unsigned long flags;
>>> + int i;
>>> + int index = -1;
>>> + size_t wcount = 0;
>>> + struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
>>> +
>>> +
>>> + if (*ppos != 0)
>>> + goto out;
>>> +
>>> + if (count > 128)
>>> + goto out;
>>> + buffer = kzalloc(128, GFP_KERNEL);
>>> +
>>> + if (!buffer)
>>> + goto out;
>> element, vmc, vmm are not initialized and you kfree them in this case
>>
> Yep, I'll fix that
>
>>> +
>>> + element = kzalloc(sizeof(buffer), GFP_KERNEL);
>>> + vmc = kzalloc(sizeof(buffer), GFP_KERNEL);
>>> + vmm = kzalloc(sizeof(buffer), GFP_KERNEL);
>> sizeof(buffer) == 4 or 8 - pretty short buffer...
>>
>>> +
>>> + if (!element || !vmm || !vmc)
>>> + goto out_free;
>>> +
>>> + wcount = count - copy_from_user(buffer, buf, count);
>>> + if (wcount < count)
>>> + goto out_free;
>> copy_from_user usage usually looks like:
>> if (copy_from_user()) {
>> ret = -EFAULT;
>> goto err;
>> }
>> you don't seem to use copy_from_user return value for anything useful
>>
> I did at one point, a few versions ago, that can likely be removed now.
>
>>> +
>>> + i = sscanf(buffer, "%s %s %s", element, vmc, vmm);
>> what if user pass strings longer than size of buffers?
>>
> You fail the write, theres a check at the top of the function for that. By the
> time you get here, buffer is guaranteed to be no more than 128 bytes.

But you allocated only 4/8 bytes (depending on size of void*) for element, vmc, vmm.
It will overflow for string like "xxxxxxxxxxxxxxxxxxx y z".

Marcin


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