Re: [PATCH 1/1] prefcnt: guard against NULL function parameters

[Alan Maguire <almagui@kernel.org>]

> When prefcnt is started without an input file, it loads the running
> kernel's debugging information through the existing vmlinux/BTF/ELF
> loading path. While walking the functions in the resulting
> compilation units, some function parameter entries can be represented
> by a NULL pointer.
> 
> refcnt_function() passes each entry from function->proto.parms to
> refcnt_parameter(). refcnt_parameter() dereferences the entry when it
> checks parameter->tag.type, causing prefcnt to terminate with a
> segmentation fault if the entry is NULL.

I still see a segmentation fault when running prefcnt on /sys/kernel/btf/vmlinux
with this change; I think the right answer here is to fix the caller by
using function__for_each_parameter() which will correctly use the ftype
to get parameters for BTF, i.e.

diff --git a/prefcnt.c b/prefcnt.c
index 37ca18f..86fceba 100644
--- a/prefcnt.c
+++ b/prefcnt.c
@@ -106,7 +106,7 @@ static void refcnt_function(struct function *function, const struct cu *cu)
                        refcnt_tag(type, cu);
        }

-       list_for_each_entry(parameter, &function->proto.parms, tag.node)
+       function__for_each_parameter(function, cu, parameter)
                refcnt_parameter(parameter, cu);

        refcnt_lexblock(&function->lexblock, cu);


Can you send a v2? Thanks!