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Binbin Deng
7a5c13cfdf
try_add_tainted_module() allocates the tracking record without zeroing
it and initializes the fields in this order:
mod_taint = kmalloc_obj(*mod_taint);
strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN);
mod_taint->taints = mod->taints;
list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
mod_taint->count = 1;
The record is published by list_add_rcu() before the count field is
written. The readers, unloaded_tainted_modules_seq_show() (debugfs,
under rcu_read_lock()) and print_unloaded_tainted_modules() (panic
path, under guard(rcu)), traverse the list under RCU and read
mod_taint->count. module_mutex, which the writer holds, does not
exclude RCU readers.
A reader that observes the new node between the list_add_rcu() and
the count store reads an uninitialized u64 left over from previous
slab use. This is a data race and leaks kernel heap residue through
the debugfs file and the panic message.
The race window is two adjacent instructions; it is reachable when a
tainted module is unloaded (rmmod) concurrently with a read of
/sys/kernel/debug/module/unloaded_tainted, or with the module list
printout of an oops on another CPU.
Fix this by initializing count before the record is published.
Found during a static-analysis-assisted audit: candidate sites were
surfaced by a Coccinelle rule, and the reader/writer paths were
confirmed by LLM-assisted (GLM-5.3) code inspection. The issue was
not observed at runtime; it is identified by code inspection only.
Fixes: 99bd995655 ("module: Introduce module unload taint tracking")
Signed-off-by: Binbin Deng <18983559317@163.com>
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
128 lines
3.1 KiB
C
128 lines
3.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Module taint unload tracking support
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*
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* Copyright (C) 2022 Aaron Tomlin
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*/
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#include <linux/module.h>
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#include <linux/string.h>
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#include <linux/printk.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#include <linux/debugfs.h>
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#include <linux/rculist.h>
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#include "internal.h"
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static LIST_HEAD(unloaded_tainted_modules);
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extern struct dentry *mod_debugfs_root;
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int try_add_tainted_module(struct module *mod)
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{
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struct mod_unload_taint *mod_taint;
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if (!mod->taints)
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goto out;
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list_for_each_entry_rcu(mod_taint, &unloaded_tainted_modules, list,
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lockdep_is_held(&module_mutex)) {
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if (!strcmp(mod_taint->name, mod->name) &&
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mod_taint->taints & mod->taints) {
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mod_taint->count++;
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goto out;
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}
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}
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mod_taint = kmalloc_obj(*mod_taint);
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if (unlikely(!mod_taint))
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return -ENOMEM;
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strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN);
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mod_taint->taints = mod->taints;
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mod_taint->count = 1;
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list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
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out:
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return 0;
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}
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void print_unloaded_tainted_modules(void)
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{
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struct mod_unload_taint *mod_taint;
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char buf[MODULE_FLAGS_BUF_SIZE];
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if (!list_empty(&unloaded_tainted_modules)) {
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printk(KERN_DEFAULT "Unloaded tainted modules:");
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list_for_each_entry_rcu(mod_taint, &unloaded_tainted_modules,
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list) {
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size_t l;
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l = module_flags_taint(mod_taint->taints, buf);
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buf[l++] = '\0';
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pr_cont(" %s(%s):%llu", mod_taint->name, buf,
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mod_taint->count);
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}
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}
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}
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#ifdef CONFIG_DEBUG_FS
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static void *unloaded_tainted_modules_seq_start(struct seq_file *m, loff_t *pos)
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__acquires(rcu)
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{
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rcu_read_lock();
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return seq_list_start_rcu(&unloaded_tainted_modules, *pos);
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}
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static void *unloaded_tainted_modules_seq_next(struct seq_file *m, void *p, loff_t *pos)
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{
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return seq_list_next_rcu(p, &unloaded_tainted_modules, pos);
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}
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static void unloaded_tainted_modules_seq_stop(struct seq_file *m, void *p)
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__releases(rcu)
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{
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rcu_read_unlock();
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}
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static int unloaded_tainted_modules_seq_show(struct seq_file *m, void *p)
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{
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struct mod_unload_taint *mod_taint;
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char buf[MODULE_FLAGS_BUF_SIZE];
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size_t l;
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mod_taint = list_entry(p, struct mod_unload_taint, list);
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l = module_flags_taint(mod_taint->taints, buf);
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buf[l++] = '\0';
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seq_printf(m, "%s (%s) %llu", mod_taint->name, buf, mod_taint->count);
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seq_puts(m, "\n");
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return 0;
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}
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static const struct seq_operations unloaded_tainted_modules_seq_ops = {
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.start = unloaded_tainted_modules_seq_start,
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.next = unloaded_tainted_modules_seq_next,
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.stop = unloaded_tainted_modules_seq_stop,
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.show = unloaded_tainted_modules_seq_show,
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};
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static int unloaded_tainted_modules_open(struct inode *inode, struct file *file)
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{
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return seq_open(file, &unloaded_tainted_modules_seq_ops);
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}
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static const struct file_operations unloaded_tainted_modules_fops = {
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.open = unloaded_tainted_modules_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release,
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};
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static int __init unloaded_tainted_modules_init(void)
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{
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debugfs_create_file("unloaded_tainted", 0444, mod_debugfs_root, NULL,
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&unloaded_tainted_modules_fops);
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return 0;
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}
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module_init(unloaded_tainted_modules_init);
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#endif /* CONFIG_DEBUG_FS */
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