sys: don't hold uts_sem while accessing userspace memory
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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/kernel/sys.c b/kernel/sys.c
index 38509dc..69b9a37 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1237,18 +1237,19 @@
SYSCALL_DEFINE1(newuname, struct new_utsname __user *, name)
{
- int errno = 0;
+ struct new_utsname tmp;
down_read(&uts_sem);
- if (copy_to_user(name, utsname(), sizeof *name))
- errno = -EFAULT;
+ memcpy(&tmp, utsname(), sizeof(tmp));
up_read(&uts_sem);
+ if (copy_to_user(name, &tmp, sizeof(tmp)))
+ return -EFAULT;
- if (!errno && override_release(name->release, sizeof(name->release)))
- errno = -EFAULT;
- if (!errno && override_architecture(name))
- errno = -EFAULT;
- return errno;
+ if (override_release(name->release, sizeof(name->release)))
+ return -EFAULT;
+ if (override_architecture(name))
+ return -EFAULT;
+ return 0;
}
#ifdef __ARCH_WANT_SYS_OLD_UNAME
@@ -1257,55 +1258,46 @@
*/
SYSCALL_DEFINE1(uname, struct old_utsname __user *, name)
{
- int error = 0;
+ struct old_utsname tmp;
if (!name)
return -EFAULT;
down_read(&uts_sem);
- if (copy_to_user(name, utsname(), sizeof(*name)))
- error = -EFAULT;
+ memcpy(&tmp, utsname(), sizeof(tmp));
up_read(&uts_sem);
+ if (copy_to_user(name, &tmp, sizeof(tmp)))
+ return -EFAULT;
- if (!error && override_release(name->release, sizeof(name->release)))
- error = -EFAULT;
- if (!error && override_architecture(name))
- error = -EFAULT;
- return error;
+ if (override_release(name->release, sizeof(name->release)))
+ return -EFAULT;
+ if (override_architecture(name))
+ return -EFAULT;
+ return 0;
}
SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
{
- int error;
+ struct oldold_utsname tmp = {};
if (!name)
return -EFAULT;
- if (!access_ok(VERIFY_WRITE, name, sizeof(struct oldold_utsname)))
- return -EFAULT;
down_read(&uts_sem);
- error = __copy_to_user(&name->sysname, &utsname()->sysname,
- __OLD_UTS_LEN);
- error |= __put_user(0, name->sysname + __OLD_UTS_LEN);
- error |= __copy_to_user(&name->nodename, &utsname()->nodename,
- __OLD_UTS_LEN);
- error |= __put_user(0, name->nodename + __OLD_UTS_LEN);
- error |= __copy_to_user(&name->release, &utsname()->release,
- __OLD_UTS_LEN);
- error |= __put_user(0, name->release + __OLD_UTS_LEN);
- error |= __copy_to_user(&name->version, &utsname()->version,
- __OLD_UTS_LEN);
- error |= __put_user(0, name->version + __OLD_UTS_LEN);
- error |= __copy_to_user(&name->machine, &utsname()->machine,
- __OLD_UTS_LEN);
- error |= __put_user(0, name->machine + __OLD_UTS_LEN);
+ memcpy(&tmp.sysname, &utsname()->sysname, __OLD_UTS_LEN);
+ memcpy(&tmp.nodename, &utsname()->nodename, __OLD_UTS_LEN);
+ memcpy(&tmp.release, &utsname()->release, __OLD_UTS_LEN);
+ memcpy(&tmp.version, &utsname()->version, __OLD_UTS_LEN);
+ memcpy(&tmp.machine, &utsname()->machine, __OLD_UTS_LEN);
up_read(&uts_sem);
+ if (copy_to_user(name, &tmp, sizeof(tmp)))
+ return -EFAULT;
- if (!error && override_architecture(name))
- error = -EFAULT;
- if (!error && override_release(name->release, sizeof(name->release)))
- error = -EFAULT;
- return error ? -EFAULT : 0;
+ if (override_architecture(name))
+ return -EFAULT;
+ if (override_release(name->release, sizeof(name->release)))
+ return -EFAULT;
+ return 0;
}
#endif
@@ -1319,17 +1311,18 @@
if (len < 0 || len > __NEW_UTS_LEN)
return -EINVAL;
- down_write(&uts_sem);
errno = -EFAULT;
if (!copy_from_user(tmp, name, len)) {
- struct new_utsname *u = utsname();
+ struct new_utsname *u;
+ down_write(&uts_sem);
+ u = utsname();
memcpy(u->nodename, tmp, len);
memset(u->nodename + len, 0, sizeof(u->nodename) - len);
errno = 0;
uts_proc_notify(UTS_PROC_HOSTNAME);
+ up_write(&uts_sem);
}
- up_write(&uts_sem);
return errno;
}
@@ -1337,8 +1330,9 @@
SYSCALL_DEFINE2(gethostname, char __user *, name, int, len)
{
- int i, errno;
+ int i;
struct new_utsname *u;
+ char tmp[__NEW_UTS_LEN + 1];
if (len < 0)
return -EINVAL;
@@ -1347,11 +1341,11 @@
i = 1 + strlen(u->nodename);
if (i > len)
i = len;
- errno = 0;
- if (copy_to_user(name, u->nodename, i))
- errno = -EFAULT;
+ memcpy(tmp, u->nodename, i);
up_read(&uts_sem);
- return errno;
+ if (copy_to_user(name, tmp, i))
+ return -EFAULT;
+ return 0;
}
#endif
@@ -1370,17 +1364,18 @@
if (len < 0 || len > __NEW_UTS_LEN)
return -EINVAL;
- down_write(&uts_sem);
errno = -EFAULT;
if (!copy_from_user(tmp, name, len)) {
- struct new_utsname *u = utsname();
+ struct new_utsname *u;
+ down_write(&uts_sem);
+ u = utsname();
memcpy(u->domainname, tmp, len);
memset(u->domainname + len, 0, sizeof(u->domainname) - len);
errno = 0;
uts_proc_notify(UTS_PROC_DOMAINNAME);
+ up_write(&uts_sem);
}
- up_write(&uts_sem);
return errno;
}
diff --git a/kernel/utsname_sysctl.c b/kernel/utsname_sysctl.c
index 233cd8f..258033d 100644
--- a/kernel/utsname_sysctl.c
+++ b/kernel/utsname_sysctl.c
@@ -18,7 +18,7 @@
#ifdef CONFIG_PROC_SYSCTL
-static void *get_uts(struct ctl_table *table, int write)
+static void *get_uts(struct ctl_table *table)
{
char *which = table->data;
struct uts_namespace *uts_ns;
@@ -26,21 +26,9 @@
uts_ns = current->nsproxy->uts_ns;
which = (which - (char *)&init_uts_ns) + (char *)uts_ns;
- if (!write)
- down_read(&uts_sem);
- else
- down_write(&uts_sem);
return which;
}
-static void put_uts(struct ctl_table *table, int write, void *which)
-{
- if (!write)
- up_read(&uts_sem);
- else
- up_write(&uts_sem);
-}
-
/*
* Special case of dostring for the UTS structure. This has locks
* to observe. Should this be in kernel/sys.c ????
@@ -50,13 +38,34 @@
{
struct ctl_table uts_table;
int r;
- memcpy(&uts_table, table, sizeof(uts_table));
- uts_table.data = get_uts(table, write);
- r = proc_dostring(&uts_table, write, buffer, lenp, ppos);
- put_uts(table, write, uts_table.data);
+ char tmp_data[__NEW_UTS_LEN + 1];
- if (write)
+ memcpy(&uts_table, table, sizeof(uts_table));
+ uts_table.data = tmp_data;
+
+ /*
+ * Buffer the value in tmp_data so that proc_dostring() can be called
+ * without holding any locks.
+ * We also need to read the original value in the write==1 case to
+ * support partial writes.
+ */
+ down_read(&uts_sem);
+ memcpy(tmp_data, get_uts(table), sizeof(tmp_data));
+ up_read(&uts_sem);
+ r = proc_dostring(&uts_table, write, buffer, lenp, ppos);
+
+ if (write) {
+ /*
+ * Write back the new value.
+ * Note that, since we dropped uts_sem, the result can
+ * theoretically be incorrect if there are two parallel writes
+ * at non-zero offsets to the same sysctl.
+ */
+ down_write(&uts_sem);
+ memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
+ up_write(&uts_sem);
proc_sys_poll_notify(table->poll);
+ }
return r;
}