linux-kernel - Re: [PATCH] Update num_symtab, symtab and strtab right after setup of core_num_syms, core_symtab and core

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Message-ID: <20100927082247.GA2463@localhost.localdomain>
Date:	Mon, 27 Sep 2010 16:22:47 +0800
From:	Hu Tao <hutao@...fujitsu.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Update num_symtab, symtab and strtab right after setup
 of core_num_syms, core_symtab and core_strtab.

On Mon, Sep 27, 2010 at 04:09:54PM +0800, Américo Wang wrote:
> On Mon, Sep 27, 2010 at 03:30:28PM +0800, Hu Tao wrote:
> >Signed-off-by: Hu Tao <hutao@...fujitsu.com>
> 
> 
> Changelog is empty.
> What bug did you observe?

symtab and strtab will point to vfreed memory after free_copy(&info)
near end of load_module().

> 
> >---
> > kernel/module.c |    9 ++++-----
> > 1 files changed, 4 insertions(+), 5 deletions(-)
> >
> >diff --git a/kernel/module.c b/kernel/module.c
> >index d0b5f8d..d5dc98b 100644
> >--- a/kernel/module.c
> >+++ b/kernel/module.c
> >@@ -2029,6 +2029,10 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> > 	for (*s = 0, i = 1; i < info->sechdrs[info->index.str].sh_size; ++i)
> > 		if (test_bit(i, info->strmap))
> > 			*++s = mod->strtab[i];
> >+
> >+	mod->num_symtab = mod->core_num_syms;
> >+	mod->symtab = mod->core_symtab;
> >+	mod->strtab = mod->core_strtab;
> > }
> > #else
> > static inline void layout_symtab(struct module *mod, struct load_info *info)
> >@@ -2738,11 +2742,6 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
> > 	/* Drop initial reference. */
> > 	module_put(mod);
> > 	trim_init_extable(mod);
> >-#ifdef CONFIG_KALLSYMS
> >-	mod->num_symtab = mod->core_num_syms;
> >-	mod->symtab = mod->core_symtab;
> >-	mod->strtab = mod->core_strtab;
> >-#endif
> > 	module_free(mod, mod->module_init);
> > 	mod->module_init = NULL;
> > 	mod->init_size = 0;
> 
> 
> This patch is not correct, symbols that are not core symbols will be
> dropped right after this piece of code. So NACK.

There is the reason why we should update num_symtab, symtab and strtab
before non-core-symbols are dropped.
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