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SubjectRe: [PATCH] of: overlay: validate offset from property fixups
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On 05/17/18 09:56, Frank Rowand wrote:
> Hi Rob,
>
> On 05/16/18 21:19, frowand.list@gmail.com wrote:
>> From: Frank Rowand <frank.rowand@sony.com>
>>
>> The smatch static checker marks the data in offset as untrusted,
>> leading it to warn:
>>
>> drivers/of/resolver.c:125 update_usages_of_a_phandle_reference()
>> error: buffer underflow 'prop->value' 's32min-s32max'
>>
>> Add check to verify that offset is within the property data.
>>
>> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
>> Signed-off-by: Frank Rowand <frank.rowand@sony.com>
>> ---
>> drivers/of/resolver.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
>> index 65d0b7adfcd4..7edfac6f1914 100644
>> --- a/drivers/of/resolver.c
>> +++ b/drivers/of/resolver.c
>> @@ -122,6 +122,11 @@ static int update_usages_of_a_phandle_reference(struct device_node *overlay,
>> goto err_fail;
>> }
>>
>> + if (offset < 0 || offset + sizeof(__be32) > prop->length) {
>> + err = -EINVAL;
>> + goto err_fail;
>> + }
>> +
>> *(__be32 *)(prop->value + offset) = cpu_to_be32(phandle);
>> }
>>
>>
>
> I should have mentioned that this results in a new compile warning
> for W=2 and W=3. The new if statement results in:
>

W=2 warning is:

> drivers/of/resolver.c:125:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

W=3 warning is:

drivers/of/resolver.c:125:3: warning: conversion to 'unsigned int' from 'int' may change the sign of the result [-Wsign-conversion]

>
> There are other pre-existing warnings in the same file for comparing
> an integer to prop->length. The correct solution is probably to
> change the type of the length field in struct property to be
> unsigned. I have added that task to my todo list.
>
> -Frank
>

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