linux-kernel - Re: Additional info on modpost segfault

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Message-ID: <m37hm6zdsr.fsf@intrepid.localdomain>
Date:	Fri, 11 Jun 2010 01:08:20 +0200
From:	Krzysztof Halasa <khc@...waw.pl>
To:	Alan <alan@...eserver.org>
Cc:	Michal Marek <mmarek@...e.cz>,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Additional info on modpost segfault

Alan <alan@...eserver.org> writes:

> program: /home/alan/GitTrees/linux-2.6-mid-ref/scripts/mod/modpost -o
> Module.symvers -S vmlinux.o
>
> Program received signal SIGSEGV, Segmentation fault.

It just hit me.
It's the offset calculation in reloc_location() which overflows:
        return (void *)elf->hdr + sechdrs[section].sh_offset +
               (r->r_offset - sechdrs[section].sh_addr);

E.g. for the first rodata r entry:
r->r_offset < sechdrs[section].sh_addr
and the expression in the parenthesis produces 0xFFFFFFE0 or something
equally wise.

Does the attached patch fix it?

Signed-off-by: Krzysztof Hałasa <khc@...waw.pl>

--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1317,8 +1317,8 @@ static unsigned int *reloc_location(struct elf_info *elf,
 	Elf_Shdr *sechdrs = elf->sechdrs;
 	int section = sechdr->sh_info;
 
 	return (void *)elf->hdr + sechdrs[section].sh_offset +
-		(r->r_offset - sechdrs[section].sh_addr);
+		r->r_offset - sechdrs[section].sh_addr;
 }
 
 static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
--
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