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    SubjectRe: [RFC][PATCH] Prevent overriding of Symbols in the Kernel, avoiding Undefined behaviour
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    Date
    On Mon, 2005-12-12 at 18:09 +0530, Ashutosh Naik wrote:
    > diff -Naurp linux-2.6.15-rc5-vanilla/kernel/module.c linux-2.6.15-rc5-mod/kernel/module.c
    > --- linux-2.6.15-rc5-vanilla/kernel/module.c 2005-12-07 19:32:23.000000000 +0530
    > +++ linux-2.6.15-rc5-mod/kernel/module.c 2005-12-12 17:47:28.000000000 +0530
    > @@ -1204,6 +1204,63 @@ void *__symbol_get(const char *symbol)
    > }
    > EXPORT_SYMBOL_GPL(__symbol_get);
    >
    > +/*
    > + * Ensure that an exported symbol [global namespace] does not already exist
    > + * in the Kernel or in some other modules exported symbol table.
    > + */
    > +static int verify_export_symbols(Elf_Shdr *sechdrs,
    > + const char *strtab,
    > + struct module *mod)
    > +{
    > + struct kernel_symbol *exportsym, *gplsym;
    > + unsigned long i,ret=0,value=0;
    > + struct module *owner;
    > + const unsigned long *crc;
    > + unsigned long index=0;
    > +
    > + spin_lock_irq(&modlist_lock);
    > +
    > + exportsym = (struct kernel_symbol *)mod->syms;
    > + gplsym = (struct kernel_symbol *)mod->gpl_syms;
    > +
    > + if (exportsym)
    > + for (i = 0; i < mod->num_syms; exportsym++,i++) {

    Hi,
    The check for exportsym not being NULL is redundant, since
    mod->num_syms will be 0 in that case. The cast is also redundant. You
    have two identical failure cases at the bottom. And your use of index
    is convoluted: do it after relocations.

    How about something like:

    const struct kernel_symbol *sym;
    unsigned int i;
    const unsigned long *crc;
    struct module *owner;

    spin_lock_irq(&modlist_lock);
    for (i = 0; i < mod->num_syms; i++)
    if (__find_symbol(mod->syms[i].name, &owner, &crc, 1))
    goto dup;
    for (i = 0; i < num->num_gpl_syms; i++)
    if (__find_symbol(mod->gpl_syms[i].name,&owner,&crc,1))
    goto dup;
    spin_unlock_irq(&modlist_lock);
    return 0;
    dup:
    printk("%s: exports duplicate symbol (owned by %s)\n",
    mod->name, module_name(owner));
    return -ENOEXEC;
    }

    Cheers,
    Rusty.
    --
    ccontrol: http://ozlabs.org/~rusty/ccontrol

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