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![David Howells](/assets/img/avatar_default.png)
This fixes CVE-2016-7042. Fix a short sprintf buffer in proc_keys_show(). If the gcc stack protector is turned on, this can cause a panic due to stack corruption. The problem is that xbuf[] is not big enough to hold a 64-bit timeout rendered as weeks: (gdb) p 0xffffffffffffffffULL/(60*60*24*7) $2 = 30500568904943 That's 14 chars plus NUL, not 11 chars plus NUL. Expand the buffer to 16 chars. I think the unpatched code apparently works if the stack-protector is not enabled because on a 32-bit machine the buffer won't be overflowed and on a 64-bit machine there's a 64-bit aligned pointer at one side and an int that isn't checked again on the other side. The panic incurred looks something like: Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: ffffffff81352ebe CPU: 0 PID: 1692 Comm: reproducer Not tainted 4.7.2-201.fc24.x86_64 #1 Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011 0000000000000086 00000000fbbd2679 ffff8800a044bc00 ffffffff813d941f ffffffff81a28d58 ffff8800a044bc98 ffff8800a044bc88 ffffffff811b2cb6 ffff880000000010 ffff8800a044bc98 ffff8800a044bc30 00000000fbbd2679 Call Trace: [<ffffffff813d941f>] dump_stack+0x63/0x84 [<ffffffff811b2cb6>] panic+0xde/0x22a [<ffffffff81352ebe>] ? proc_keys_show+0x3ce/0x3d0 [<ffffffff8109f7f9>] __stack_chk_fail+0x19/0x30 [<ffffffff81352ebe>] proc_keys_show+0x3ce/0x3d0 [<ffffffff81350410>] ? key_validate+0x50/0x50 [<ffffffff8134db30>] ? key_default_cmp+0x20/0x20 [<ffffffff8126b31c>] seq_read+0x2cc/0x390 [<ffffffff812b6b12>] proc_reg_read+0x42/0x70 [<ffffffff81244fc7>] __vfs_read+0x37/0x150 [<ffffffff81357020>] ? security_file_permission+0xa0/0xc0 [<ffffffff81246156>] vfs_read+0x96/0x130 [<ffffffff81247635>] SyS_read+0x55/0xc0 [<ffffffff817eb872>] entry_SYSCALL_64_fastpath+0x1a/0xa4 Reported-by: Ondrej Kozina <okozina@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Ondrej Kozina <okozina@redhat.com> cc: stable@vger.kernel.org Signed-off-by: James Morris <james.l.morris@oracle.com>
352 lines
8.7 KiB
C
352 lines
8.7 KiB
C
/* procfs files for key database enumeration
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*
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* Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/sched.h>
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#include <linux/fs.h>
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#include <linux/proc_fs.h>
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#include <linux/seq_file.h>
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#include <asm/errno.h>
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#include "internal.h"
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static int proc_keys_open(struct inode *inode, struct file *file);
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static void *proc_keys_start(struct seq_file *p, loff_t *_pos);
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static void *proc_keys_next(struct seq_file *p, void *v, loff_t *_pos);
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static void proc_keys_stop(struct seq_file *p, void *v);
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static int proc_keys_show(struct seq_file *m, void *v);
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static const struct seq_operations proc_keys_ops = {
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.start = proc_keys_start,
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.next = proc_keys_next,
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.stop = proc_keys_stop,
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.show = proc_keys_show,
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};
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static const struct file_operations proc_keys_fops = {
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.open = proc_keys_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 proc_key_users_open(struct inode *inode, struct file *file);
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static void *proc_key_users_start(struct seq_file *p, loff_t *_pos);
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static void *proc_key_users_next(struct seq_file *p, void *v, loff_t *_pos);
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static void proc_key_users_stop(struct seq_file *p, void *v);
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static int proc_key_users_show(struct seq_file *m, void *v);
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static const struct seq_operations proc_key_users_ops = {
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.start = proc_key_users_start,
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.next = proc_key_users_next,
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.stop = proc_key_users_stop,
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.show = proc_key_users_show,
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};
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static const struct file_operations proc_key_users_fops = {
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.open = proc_key_users_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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/*
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* Declare the /proc files.
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*/
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static int __init key_proc_init(void)
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{
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struct proc_dir_entry *p;
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p = proc_create("keys", 0, NULL, &proc_keys_fops);
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if (!p)
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panic("Cannot create /proc/keys\n");
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p = proc_create("key-users", 0, NULL, &proc_key_users_fops);
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if (!p)
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panic("Cannot create /proc/key-users\n");
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return 0;
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}
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__initcall(key_proc_init);
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/*
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* Implement "/proc/keys" to provide a list of the keys on the system that
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* grant View permission to the caller.
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*/
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static struct rb_node *key_serial_next(struct seq_file *p, struct rb_node *n)
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{
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struct user_namespace *user_ns = seq_user_ns(p);
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n = rb_next(n);
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while (n) {
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struct key *key = rb_entry(n, struct key, serial_node);
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if (kuid_has_mapping(user_ns, key->user->uid))
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break;
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n = rb_next(n);
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}
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return n;
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}
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static int proc_keys_open(struct inode *inode, struct file *file)
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{
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return seq_open(file, &proc_keys_ops);
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}
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static struct key *find_ge_key(struct seq_file *p, key_serial_t id)
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{
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struct user_namespace *user_ns = seq_user_ns(p);
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struct rb_node *n = key_serial_tree.rb_node;
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struct key *minkey = NULL;
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while (n) {
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struct key *key = rb_entry(n, struct key, serial_node);
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if (id < key->serial) {
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if (!minkey || minkey->serial > key->serial)
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minkey = key;
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n = n->rb_left;
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} else if (id > key->serial) {
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n = n->rb_right;
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} else {
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minkey = key;
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break;
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}
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key = NULL;
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}
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if (!minkey)
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return NULL;
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for (;;) {
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if (kuid_has_mapping(user_ns, minkey->user->uid))
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return minkey;
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n = rb_next(&minkey->serial_node);
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if (!n)
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return NULL;
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minkey = rb_entry(n, struct key, serial_node);
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}
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}
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static void *proc_keys_start(struct seq_file *p, loff_t *_pos)
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__acquires(key_serial_lock)
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{
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key_serial_t pos = *_pos;
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struct key *key;
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spin_lock(&key_serial_lock);
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if (*_pos > INT_MAX)
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return NULL;
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key = find_ge_key(p, pos);
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if (!key)
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return NULL;
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*_pos = key->serial;
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return &key->serial_node;
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}
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static inline key_serial_t key_node_serial(struct rb_node *n)
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{
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struct key *key = rb_entry(n, struct key, serial_node);
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return key->serial;
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}
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static void *proc_keys_next(struct seq_file *p, void *v, loff_t *_pos)
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{
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struct rb_node *n;
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n = key_serial_next(p, v);
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if (n)
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*_pos = key_node_serial(n);
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return n;
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}
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static void proc_keys_stop(struct seq_file *p, void *v)
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__releases(key_serial_lock)
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{
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spin_unlock(&key_serial_lock);
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}
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static int proc_keys_show(struct seq_file *m, void *v)
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{
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struct rb_node *_p = v;
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struct key *key = rb_entry(_p, struct key, serial_node);
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struct timespec now;
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unsigned long timo;
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key_ref_t key_ref, skey_ref;
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char xbuf[16];
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int rc;
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struct keyring_search_context ctx = {
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.index_key.type = key->type,
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.index_key.description = key->description,
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.cred = current_cred(),
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.match_data.cmp = lookup_user_key_possessed,
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.match_data.raw_data = key,
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.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
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.flags = KEYRING_SEARCH_NO_STATE_CHECK,
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};
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key_ref = make_key_ref(key, 0);
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/* determine if the key is possessed by this process (a test we can
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* skip if the key does not indicate the possessor can view it
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*/
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if (key->perm & KEY_POS_VIEW) {
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skey_ref = search_my_process_keyrings(&ctx);
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if (!IS_ERR(skey_ref)) {
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key_ref_put(skey_ref);
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key_ref = make_key_ref(key, 1);
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}
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}
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/* check whether the current task is allowed to view the key (assuming
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* non-possession)
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* - the caller holds a spinlock, and thus the RCU read lock, making our
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* access to __current_cred() safe
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*/
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rc = key_task_permission(key_ref, ctx.cred, KEY_NEED_VIEW);
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if (rc < 0)
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return 0;
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now = current_kernel_time();
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rcu_read_lock();
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/* come up with a suitable timeout value */
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if (key->expiry == 0) {
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memcpy(xbuf, "perm", 5);
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} else if (now.tv_sec >= key->expiry) {
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memcpy(xbuf, "expd", 5);
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} else {
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timo = key->expiry - now.tv_sec;
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if (timo < 60)
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sprintf(xbuf, "%lus", timo);
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else if (timo < 60*60)
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sprintf(xbuf, "%lum", timo / 60);
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else if (timo < 60*60*24)
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sprintf(xbuf, "%luh", timo / (60*60));
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else if (timo < 60*60*24*7)
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sprintf(xbuf, "%lud", timo / (60*60*24));
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else
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sprintf(xbuf, "%luw", timo / (60*60*24*7));
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}
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#define showflag(KEY, LETTER, FLAG) \
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(test_bit(FLAG, &(KEY)->flags) ? LETTER : '-')
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seq_printf(m, "%08x %c%c%c%c%c%c%c %5d %4s %08x %5d %5d %-9.9s ",
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key->serial,
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showflag(key, 'I', KEY_FLAG_INSTANTIATED),
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showflag(key, 'R', KEY_FLAG_REVOKED),
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showflag(key, 'D', KEY_FLAG_DEAD),
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showflag(key, 'Q', KEY_FLAG_IN_QUOTA),
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showflag(key, 'U', KEY_FLAG_USER_CONSTRUCT),
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showflag(key, 'N', KEY_FLAG_NEGATIVE),
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showflag(key, 'i', KEY_FLAG_INVALIDATED),
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atomic_read(&key->usage),
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xbuf,
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key->perm,
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from_kuid_munged(seq_user_ns(m), key->uid),
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from_kgid_munged(seq_user_ns(m), key->gid),
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key->type->name);
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#undef showflag
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if (key->type->describe)
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key->type->describe(key, m);
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seq_putc(m, '\n');
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rcu_read_unlock();
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return 0;
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}
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static struct rb_node *__key_user_next(struct user_namespace *user_ns, struct rb_node *n)
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{
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while (n) {
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struct key_user *user = rb_entry(n, struct key_user, node);
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if (kuid_has_mapping(user_ns, user->uid))
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break;
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n = rb_next(n);
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}
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return n;
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}
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static struct rb_node *key_user_next(struct user_namespace *user_ns, struct rb_node *n)
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{
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return __key_user_next(user_ns, rb_next(n));
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}
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static struct rb_node *key_user_first(struct user_namespace *user_ns, struct rb_root *r)
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{
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struct rb_node *n = rb_first(r);
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return __key_user_next(user_ns, n);
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}
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/*
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* Implement "/proc/key-users" to provides a list of the key users and their
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* quotas.
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*/
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static int proc_key_users_open(struct inode *inode, struct file *file)
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{
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return seq_open(file, &proc_key_users_ops);
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}
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static void *proc_key_users_start(struct seq_file *p, loff_t *_pos)
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__acquires(key_user_lock)
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{
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struct rb_node *_p;
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loff_t pos = *_pos;
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spin_lock(&key_user_lock);
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_p = key_user_first(seq_user_ns(p), &key_user_tree);
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while (pos > 0 && _p) {
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pos--;
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_p = key_user_next(seq_user_ns(p), _p);
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}
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return _p;
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}
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static void *proc_key_users_next(struct seq_file *p, void *v, loff_t *_pos)
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{
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(*_pos)++;
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return key_user_next(seq_user_ns(p), (struct rb_node *)v);
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}
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static void proc_key_users_stop(struct seq_file *p, void *v)
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__releases(key_user_lock)
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{
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spin_unlock(&key_user_lock);
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}
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static int proc_key_users_show(struct seq_file *m, void *v)
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{
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struct rb_node *_p = v;
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struct key_user *user = rb_entry(_p, struct key_user, node);
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unsigned maxkeys = uid_eq(user->uid, GLOBAL_ROOT_UID) ?
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key_quota_root_maxkeys : key_quota_maxkeys;
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unsigned maxbytes = uid_eq(user->uid, GLOBAL_ROOT_UID) ?
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key_quota_root_maxbytes : key_quota_maxbytes;
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seq_printf(m, "%5u: %5d %d/%d %d/%d %d/%d\n",
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from_kuid_munged(seq_user_ns(m), user->uid),
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atomic_read(&user->usage),
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atomic_read(&user->nkeys),
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atomic_read(&user->nikeys),
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user->qnkeys,
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maxkeys,
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user->qnbytes,
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maxbytes);
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return 0;
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}
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