linux-kernel - [16/17] kbuild: Fix modpost segfault

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Message-Id: <20100730165955.213082095@clark.site>
Date:	Fri, 30 Jul 2010 09:57:32 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Krzysztof HaÅasa <khc@...waw.pl>,
	Michal Marek <mmarek@...e.cz>
Subject: [16/17] kbuild: Fix modpost segfault

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Krzysztof Halasa <khc@...waw.pl>

commit 1c938663d58b5b2965976a6f54cc51b5d6f691aa upstream.

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.

Reported-by: Alan <alan@...eserver.org>
Signed-off-by: Krzysztof Hałasa <khc@...waw.pl>
Tested-by: Alan <alan@...eserver.org>
Signed-off-by: Michal Marek <mmarek@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 scripts/mod/modpost.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1292,7 +1292,7 @@ static unsigned int *reloc_location(stru
 	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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