linux-kernel - Re: [ 11/83] module: fix out-by-one error in kallsyms

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Message-ID: <87hao4j91l.fsf@rustcorp.com.au>
Date:	Mon, 03 Dec 2012 10:34:06 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	satoru takeuchi <satoru.takeuchi@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	alan@...rguk.ukuu.org.uk,
	Masaki Kimura <masaki.kimura.kz@...achi.com>
Subject: Re: [ 11/83] module: fix out-by-one error in kallsyms

satoru takeuchi <satoru.takeuchi@...il.com> writes:
> Hi,

Hi!

>> --- a/kernel/module.c
>> +++ b/kernel/module.c
>> @@ -2273,12 +2273,17 @@ static void layout_symtab(struct module
>>         src = (void *)info->hdr + symsect->sh_offset;
>>         nsrc = symsect->sh_size / sizeof(*src);
>>
>> +       /* strtab always starts with a nul, so offset 0 is the empty string. */
>> +       strtab_size = 1;
>> +
>
> I suspect above code sniped is not needed since the size of src[0](always 1) is
> counted at the following code("strtab_size += strlen(..) + 1;").

You are correct, on both counts.  This was a remnant of the previous
1-based looping.

Here's the fix I have pending.

Thanks!
Rusty.

module: fix one byte kallsyms overallocation.

Since we fixed our kallsyms strtab expansion code in
59ef28b1f14899b10d6b2682c7057ca00a9a3f47 (module: fix out-by-one error
in kallsyms) we now loop from zero, so we don't need to add an extra
byte for the first empty string.

Reported-by: satoru takeuchi <satoru.takeuchi@...il.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff --git a/kernel/module.c b/kernel/module.c
index a1d2ed8..79a526d 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2285,7 +2285,7 @@ static void layout_symtab(struct module *mod, struct load_info *info)
 	Elf_Shdr *symsect = info->sechdrs + info->index.sym;
 	Elf_Shdr *strsect = info->sechdrs + info->index.str;
 	const Elf_Sym *src;
-	unsigned int i, nsrc, ndst, strtab_size;
+	unsigned int i, nsrc, ndst, strtab_size = 0;
 
 	/* Put symbol section at end of init part of module. */
 	symsect->sh_flags |= SHF_ALLOC;
@@ -2296,9 +2296,6 @@ static void layout_symtab(struct module *mod, struct load_info *info)
 	src = (void *)info->hdr + symsect->sh_offset;
 	nsrc = symsect->sh_size / sizeof(*src);
 
-	/* strtab always starts with a nul, so offset 0 is the empty string. */
-	strtab_size = 1;
-
 	/* Compute total space required for the core symbols' strtab. */
 	for (ndst = i = 0; i < nsrc; i++) {
 		if (i == 0 ||
@@ -2340,7 +2337,6 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 	mod->core_symtab = dst = mod->module_core + info->symoffs;
 	mod->core_strtab = s = mod->module_core + info->stroffs;
 	src = mod->symtab;
-	*s++ = 0;
 	for (ndst = i = 0; i < mod->num_symtab; i++) {
 		if (i == 0 ||
 		    is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum)) {
--
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