On 11/01/2021 13:55, Maximilian Luz wrote:
> On 1/11/21 1:12 PM, Colin Ian King wrote:
>> Hi Maximilian,
>>
>> Static analysis of linux-next with Coverity has found several issues
>> with the following commit:
>>
>> commit 178f6ab77e617c984d6520b92e747075a12676ff
>> Author: Maximilian Luz <luzmaximilian@xxxxxxxxx>
>> Date: Mon Dec 21 19:39:58 2020 +0100
>>
>> platform/surface: Add Surface Aggregator user-space interface
>>
>> The analysis is as follows:
>>
>> 65static long ssam_cdev_request(struct ssam_cdev *cdev, unsigned long
>> arg)
>> 66{
>> 67 struct ssam_cdev_request __user *r;
>> 68 struct ssam_cdev_request rqst;
>>
>> 1. var_decl: Declaring variable spec without initializer.
>>
>> 69 struct ssam_request spec;
>> 70 struct ssam_response rsp;
>> 71 const void __user *plddata;
>> 72 void __user *rspdata;
>> 73 int status = 0, ret = 0, tmp;
>> 74
>> 75 r = (struct ssam_cdev_request __user *)arg;
>> 76 ret = copy_struct_from_user(&rqst, sizeof(rqst), r,
>> sizeof(*r));
>>
>> 2. Condition ret, taking true branch.
>>
>> 77 if (ret)
>>
>> 3. Jumping to label out.
>>
>> 78 goto out;
>>
>> 79
>> 80 plddata = u64_to_user_ptr(rqst.payload.data);
>> 81 rspdata = u64_to_user_ptr(rqst.response.data);
>> 82
>> 83 /* Setup basic request fields. */
>> 84 spec.target_category = rqst.target_category;
>> 85 spec.target_id = rqst.target_id;
>> 86 spec.command_id = rqst.command_id;
>> 87 spec.instance_id = rqst.instance_id;
>> 88 spec.flags = 0;
>> 89 spec.length = rqst.payload.length;
>> 90 spec.payload = NULL;
>> 91
>> 92 if (rqst.flags & SSAM_CDEV_REQUEST_HAS_RESPONSE)
>> 93 spec.flags |= SSAM_REQUEST_HAS_RESPONSE;
>> 94
>> 95 if (rqst.flags & SSAM_CDEV_REQUEST_UNSEQUENCED)
>> 96 spec.flags |= SSAM_REQUEST_UNSEQUENCED;
>> 97
>> 98 rsp.capacity = rqst.response.length;
>> 99 rsp.length = 0;
>> 100 rsp.pointer = NULL;
>> 101
>> 102 /* Get request payload from user-space. */
>> 103 if (spec.length) {
>> 104 if (!plddata) {
>> 105 ret = -EINVAL;
>> 106 goto out;
>> 107 }
>> 108
>>
>> CID: Untrusted allocation size (TAINTED_SCALAR)
>> 8. tainted_data: Passing tainted expression spec.length to kzalloc,
>> which uses it as an allocation size
>>
>> 109 spec.payload = kzalloc(spec.length, GFP_KERNEL);
>
> I assume a constraint on the maximum length will fix this?
I believe so, it's unsigned so just an upper size check will be required
to silence this static analysis warning. Mind you, you may want a size
that is the full u16 max of 65535, so in that case the check is not
required.
>
>> 110 if (!spec.payload) {
>> 111 ret = -ENOMEM;
>> 112 goto out;
>> 113 }
>> 114
>> 115 if (copy_from_user((void *)spec.payload, plddata,
>> spec.length)) {
>> 116 ret = -EFAULT;
>> 117 goto out;
>> 118 }
>> 119 }
>> 120
>> 121 /* Allocate response buffer. */
>> 122 if (rsp.capacity) {
>> 123 if (!rspdata) {
>> 124 ret = -EINVAL;
>> 125 goto out;
>> 126 }
>> 127
>>
>> CID: Untrusted allocation size (TAINTED_SCALAR)
>> 12. tainted_data: Passing tainted expression rsp.capacity to kzalloc,
>> which uses it as an allocation size
>>
>> 128 rsp.pointer = kzalloc(rsp.capacity, GFP_KERNEL);
>> 129 if (!rsp.pointer) {
>> 130 ret = -ENOMEM;
>> 131 goto out;
>> 132 }
>> 133 }
>> 134
>> 135 /* Perform request. */
>> 136 status = ssam_request_sync(cdev->ctrl, &spec, &rsp);
>> 137 if (status)
>> 138 goto out;
>> 139
>> 140 /* Copy response to user-space. */
>> 141 if (rsp.length && copy_to_user(rspdata, rsp.pointer,
>> rsp.length))
>> 142 ret = -EFAULT;
>> 143
>> 144out:
>> 145 /* Always try to set response-length and status. */
>>
>> CID: Uninitialized pointer read (UNINIT)
>> Using uninitialized value rsp.length
>>
>> 146 tmp = put_user(rsp.length, &r->response.length);
>>
>> 4. Condition tmp, taking true branch.
>>
>> 147 if (tmp)
>> 148 ret = tmp;
>> 149
>> 150 tmp = put_user(status, &r->status);
>>
>> 5. Condition tmp, taking true branch.
>>
>> 151 if (tmp)
>> 152 ret = tmp;
>> 153
>> 154 /* Cleanup. */
>>
>> CID: Uninitialized pointer read (UNINIT)
>> 6. uninit_use_in_call: Using uninitialized value spec.payload when
>> calling kfree.
>>
>> 155 kfree(spec.payload);
>>
>> CID: Uninitialized pointer read (UNINIT)
>> uninit_use_in_call: Using uninitialized value rsp.pointer when
>> calling kfree
>>
>> 156 kfree(rsp.pointer);
>
> Right, taking the first jump to out leaves rsp and spec uninitialized.
> I'll fix that.
>
>> 157
>> 158 return ret;
>>
>> Colin
>>
>
> Thank you for the analysis. I'll draft up two patches to address these
> issues.
>
> Regards,
> Max
