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Subject[PATCH 2/2] taskstats: restrict access to user
Date
taskstats information may be used for gathering private information.
E.g. for openssh and vsftpd daemons read_characters/write_characters may
be used to learn the precise password length. Restrict it to processes
being able to ptrace the target process.

For TASKSTATS_CMD_ATTR_REGISTER_CPUMASK the fix is euid check instead of
a ptrace check as the handler is processed in the context of the target
process, not the listener process'. When ptrace_task_may_access_current()
is introduced, it should be used instead of euid check. Currently there
is a small race when a process temporarily changes its euid (e.g. to
access user's files), until the process sets euid back user's processes
may gather privileged process' statistics.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
---
kernel/taskstats.c | 23 ++++++++++++++++++++++-
1 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 9ffea36..d92c95a 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -27,6 +27,7 @@
#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/file.h>
+#include <linux/ptrace.h>
#include <net/genetlink.h>
#include <asm/atomic.h>

@@ -132,6 +133,8 @@ static void send_cpu_listeners(struct sk_buff *skb,
struct sk_buff *skb_next, *skb_cur = skb;
void *reply = genlmsg_data(genlhdr);
int rc, delcount = 0;
+ const struct cred *cred = current_cred();
+ struct task_struct *task;

rc = genlmsg_end(skb, reply);
if (rc < 0) {
@@ -142,6 +145,15 @@ static void send_cpu_listeners(struct sk_buff *skb,
rc = 0;
down_read(&listeners->sem);
list_for_each_entry(s, &listeners->list, list) {
+
+ rcu_read_lock();
+ task = find_task_by_vpid(s->pid);
+ if (!task || __task_cred(task)->euid != cred->euid) {
+ rcu_read_unlock();
+ continue;
+ }
+ rcu_read_unlock();
+
skb_next = NULL;
if (!list_is_last(&s->list, &listeners->list)) {
skb_next = skb_clone(skb_cur, GFP_KERNEL);
@@ -199,14 +211,19 @@ static void fill_stats(struct task_struct *tsk, struct taskstats *stats)
static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
{
struct task_struct *tsk;
+ int rc = -ESRCH;

rcu_read_lock();
tsk = find_task_by_vpid(pid);
+ if (tsk && !ptrace_may_access(tsk, PTRACE_MODE_READ)) {
+ tsk = NULL;
+ rc = -EACCES;
+ }
if (tsk)
get_task_struct(tsk);
rcu_read_unlock();
if (!tsk)
- return -ESRCH;
+ return rc;
fill_stats(tsk, stats);
put_task_struct(tsk);
return 0;
@@ -224,6 +241,10 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
*/
rcu_read_lock();
first = find_task_by_vpid(tgid);
+ if (first && !ptrace_may_access(first, PTRACE_MODE_READ)) {
+ rc = -EACCES;
+ goto out;
+ }

if (!first || !lock_task_sighand(first, &flags))
goto out;
--
1.7.0.4


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