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42a0cc3478
Holding uts_sem as a writer while accessing userspace memory allows a
namespace admin to stall all processes that attempt to take uts_sem.
Instead, move data through stack buffers and don't access userspace memory
while uts_sem is held.
Cc: stable@vger.kernel.org
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
149 lines
3.4 KiB
C
149 lines
3.4 KiB
C
/*
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* Copyright (C) 2007
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*
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* Author: Eric Biederman <ebiederm@xmision.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 as
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* published by the Free Software Foundation, version 2 of the
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* License.
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*/
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#include <linux/export.h>
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#include <linux/uts.h>
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#include <linux/utsname.h>
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#include <linux/sysctl.h>
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#include <linux/wait.h>
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#include <linux/rwsem.h>
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#ifdef CONFIG_PROC_SYSCTL
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static void *get_uts(struct ctl_table *table)
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{
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char *which = table->data;
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struct uts_namespace *uts_ns;
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uts_ns = current->nsproxy->uts_ns;
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which = (which - (char *)&init_uts_ns) + (char *)uts_ns;
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return which;
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}
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/*
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* Special case of dostring for the UTS structure. This has locks
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* to observe. Should this be in kernel/sys.c ????
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*/
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static int proc_do_uts_string(struct ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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struct ctl_table uts_table;
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int r;
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char tmp_data[__NEW_UTS_LEN + 1];
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memcpy(&uts_table, table, sizeof(uts_table));
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uts_table.data = tmp_data;
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/*
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* Buffer the value in tmp_data so that proc_dostring() can be called
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* without holding any locks.
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* We also need to read the original value in the write==1 case to
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* support partial writes.
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*/
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down_read(&uts_sem);
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memcpy(tmp_data, get_uts(table), sizeof(tmp_data));
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up_read(&uts_sem);
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r = proc_dostring(&uts_table, write, buffer, lenp, ppos);
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if (write) {
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/*
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* Write back the new value.
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* Note that, since we dropped uts_sem, the result can
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* theoretically be incorrect if there are two parallel writes
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* at non-zero offsets to the same sysctl.
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*/
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down_write(&uts_sem);
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memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
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up_write(&uts_sem);
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proc_sys_poll_notify(table->poll);
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}
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return r;
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}
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#else
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#define proc_do_uts_string NULL
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#endif
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static DEFINE_CTL_TABLE_POLL(hostname_poll);
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static DEFINE_CTL_TABLE_POLL(domainname_poll);
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static struct ctl_table uts_kern_table[] = {
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{
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.procname = "ostype",
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.data = init_uts_ns.name.sysname,
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.maxlen = sizeof(init_uts_ns.name.sysname),
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.mode = 0444,
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.proc_handler = proc_do_uts_string,
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},
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{
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.procname = "osrelease",
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.data = init_uts_ns.name.release,
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.maxlen = sizeof(init_uts_ns.name.release),
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.mode = 0444,
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.proc_handler = proc_do_uts_string,
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},
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{
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.procname = "version",
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.data = init_uts_ns.name.version,
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.maxlen = sizeof(init_uts_ns.name.version),
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.mode = 0444,
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.proc_handler = proc_do_uts_string,
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},
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{
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.procname = "hostname",
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.data = init_uts_ns.name.nodename,
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.maxlen = sizeof(init_uts_ns.name.nodename),
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.mode = 0644,
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.proc_handler = proc_do_uts_string,
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.poll = &hostname_poll,
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},
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{
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.procname = "domainname",
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.data = init_uts_ns.name.domainname,
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.maxlen = sizeof(init_uts_ns.name.domainname),
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.mode = 0644,
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.proc_handler = proc_do_uts_string,
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.poll = &domainname_poll,
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},
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{}
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};
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static struct ctl_table uts_root_table[] = {
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{
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.procname = "kernel",
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.mode = 0555,
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.child = uts_kern_table,
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},
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{}
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};
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#ifdef CONFIG_PROC_SYSCTL
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/*
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* Notify userspace about a change in a certain entry of uts_kern_table,
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* identified by the parameter proc.
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*/
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void uts_proc_notify(enum uts_proc proc)
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{
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struct ctl_table *table = &uts_kern_table[proc];
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proc_sys_poll_notify(table->poll);
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}
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#endif
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static int __init utsname_sysctl_init(void)
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{
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register_sysctl_table(uts_root_table);
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return 0;
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}
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device_initcall(utsname_sysctl_init);
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