Messages in this thread Patch in this message | | | Date | Tue, 13 Dec 2005 19:56:07 +0530 | From | Ashutosh Naik <> | Subject | Re: [RFC][PATCH] Prevent overriding of Symbols in the Kernel, avoiding Undefined behaviour |
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On 12/13/05, Rusty Russell <rusty@rustcorp.com.au> wrote: > > 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; > }
Have tried that in the attached patch. However, mod->syms[i].name would be valid only after a long relocation for loop has run through. While this adds a wee bit extra overhead, that overhead is only in the case where the module does actually export a Duplicate Symbol.
This its a question, whether we do the search before relocation ( A little messier ) or after ( More straight forward)
Regards Ashutosh --- /usr/src/linux-2.6.15-rc5-vanilla/kernel/module.c 2005-12-07 19:32:23.000000000 +0530 +++ /usr/src/linux-2.6.15-rc5/kernel/module.c 2005-12-13 19:44:43.000000000 +0530 @@ -1204,6 +1204,42 @@ 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(struct module *mod) +{ + const char *name=0; + unsigned long i, ret = 0; + struct module *owner; + const unsigned long *crc; + + spin_lock_irq(&modlist_lock); + for (i = 0; i < mod->num_syms; i++) + if (unlikely(__find_symbol(mod->syms[i].name, &owner, &crc,1))) { + name = mod->syms[i].name; + ret = -ENOEXEC; + goto dup; + } + + for (i = 0; i < mod->num_gpl_syms; i++) + if (unlikely(__find_symbol(mod->gpl_syms[i].name, &owner, &crc,1))) { + name = mod->gpl_syms[i].name; + ret = -ENOEXEC; + goto dup; + } + +dup: + spin_unlock_irq(&modlist_lock); + + if (ret) + printk("%s: exports duplicate symbol %s (owned by %s)\n", + mod->name, name, module_name(owner)); + + return ret; +} + /* Change all symbols so that sh_value encodes the pointer directly. */ static int simplify_symbols(Elf_Shdr *sechdrs, unsigned int symindex, @@ -1767,6 +1804,12 @@ static struct module *load_module(void _ goto cleanup; } + /* Find duplicate symbols */ + err = verify_export_symbols(mod); + + if (err < 0) + goto cleanup; + /* Set up and sort exception table */ mod->num_exentries = sechdrs[exindex].sh_size / sizeof(*mod->extable); mod->extable = extable = (void *)sechdrs[exindex].sh_addr;
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