[PATCH] pid_ns: ensure pid is not freed during kill_pid_in..

Alan Stern points out that after spin_unlock(&ps->lock) there is no
guarantee that ps->pid won't be freed. Since kill_pid_info_as_uid() is
called after the spin_unlock(), the pid passed to it must be pinned.

Signed-off-by: Serge Hallyn
---
drivers/usb/core/devio.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 37518df..eea53eb 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -407,7 +407,7 @@ static void async_completed(struct urb *urb)
sinfo.si_errno = as->status;
sinfo.si_code = SI_ASYNCIO;
sinfo.si_addr = as->userurb;
- pid = as->pid;
+ pid = get_pid(as->pid);
uid = as->uid;
euid = as->euid;
secid = as->secid;
@@ -422,9 +422,11 @@ static void async_completed(struct urb *urb)
cancel_bulk_urbs(ps, as->bulk_addr);
spin_unlock(&ps->lock);

- if (signr)
+ if (signr) {
kill_pid_info_as_uid(sinfo.si_signo, &sinfo, pid, uid,
euid, secid);
+ put_pid(pid);
+ }

wake_up(&ps->wait);
}
--
1.7.0.4

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Add to the dev_state and alloc_async structures the user namespace
corresponding to the uid and euid. Pass these to kill_pid_info_as_uid(),
which can then implement a proper, user-namespace-aware uid check.

Changelog:
Sep 20: Per Oleg's suggestion: Instead of caching and passing user namespace,
uid, and euid each separately, pass a struct cred.
Sep 26: Address Alan Stern's comments: don't define a struct cred at
usbdev_open(), and take and put a cred at async_completed() to
ensure it lasts for the duration of kill_pid_info_as_cred().

Signed-off-by: Serge Hallyn
Cc: Greg KH
Cc: Oleg Nesterov
Cc: "Eric W. Biederman"
Cc: Tejun Heo
---
drivers/usb/core/devio.c | 30 +++++++++++++-----------------
include/linux/sched.h | 3 ++-
kernel/signal.c | 24 ++++++++++++++++--------
3 files changed, 31 insertions(+), 26 deletions(-)

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index eea53eb..000c25d 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -46,6 +46,7 @@
#include <linux/cdev.h>
#include <linux/notifier.h>
#include <linux/security.h>
+#include <linux/user_namespace.h>
#include <asm/uaccess.h>
#include <asm/byteorder.h>
#include <linux/moduleparam.h>
@@ -68,7 +69,7 @@ struct dev_state {
wait_queue_head_t wait; /* wake up if a request completed */
unsigned int discsignr;
struct pid *disc_pid;
- uid_t disc_uid, disc_euid;
+ const struct cred *cred;
void __user *disccontext;
unsigned long ifclaimed;
u32 secid;
@@ -79,7 +80,7 @@ struct async {
struct list_head asynclist;
struct dev_state *ps;
struct pid *pid;
- uid_t uid, euid;
+ const struct cred *cred;
unsigned int signr;
unsigned int ifnum;
void __user *userbuffer;
@@ -248,6 +249,7 @@ static struct async *alloc_async(unsigned int numisoframes)
static void free_async(struct async *as)
{
put_pid(as->pid);
+ put_cred(as->cred);
kfree(as->urb->transfer_buffer);
kfree(as->urb->setup_packet);
usb_free_urb(as->urb);
@@ -393,9 +395,8 @@ static void async_completed(struct urb *urb)
struct dev_state *ps = as->ps;
struct siginfo sinfo;
struct pid *pid = NULL;
- uid_t uid = 0;
- uid_t euid = 0;
u32 secid = 0;
+ const struct cred *cred = NULL;
int signr;

spin_lock(&ps->lock);
@@ -408,8 +409,7 @@ static void async_completed(struct urb *urb)
sinfo.si_code = SI_ASYNCIO;
sinfo.si_addr = as->userurb;
pid = get_pid(as->pid);
- uid = as->uid;
- euid = as->euid;
+ cred = get_cred(as->cred);
secid = as->secid;
}
snoop(&urb->dev->dev, "urb complete\n");
@@ -423,9 +423,9 @@ static void async_completed(struct urb *urb)
spin_unlock(&ps->lock);

if (signr) {
- kill_pid_info_as_uid(sinfo.si_signo, &sinfo, pid, uid,
- euid, secid);
+ kill_pid_info_as_cred(sinfo.si_signo, &sinfo, pid, cred, secid);
put_pid(pid);
+ put_cred(cred);
}

wake_up(&ps->wait);
@@ -658,7 +658,6 @@ static int usbdev_open(struct inode *inode, struct file *file)
{
struct usb_device *dev = NULL;
struct dev_state *ps;
- const struct cred *cred = current_cred();
int ret;

ret = -ENOMEM;
@@ -708,8 +707,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
init_waitqueue_head(&ps->wait);
ps->discsignr = 0;
ps->disc_pid = get_pid(task_pid(current));
- ps->disc_uid = cred->uid;
- ps->disc_euid = cred->euid;
+ ps->cred = get_current_cred();
ps->disccontext = NULL;
ps->ifclaimed = 0;
security_task_getsecid(current, &ps->secid);
@@ -751,6 +749,7 @@ static int usbdev_release(struct inode *inode, struct file *file)
usb_unlock_device(dev);
usb_put_dev(dev);
put_pid(ps->disc_pid);
+ put_cred(ps->cred);

as = async_getcompleted(ps);
while (as) {
@@ -1050,7 +1049,6 @@ static int proc_do_submiturb(struct dev_state *ps, struct usbdevfs_urb *uurb,
struct usb_host_endpoint *ep;
struct async *as;
struct usb_ctrlrequest *dr = NULL;
- const struct cred *cred = current_cred();
unsigned int u, totlen, isofrmlen;
int ret, ifnum = -1;
int is_in;
@@ -1264,8 +1262,7 @@ static int proc_do_submiturb(struct dev_state *ps, struct usbdevfs_urb *uurb,
as->signr = uurb->signr;
as->ifnum = ifnum;
as->pid = get_pid(task_pid(current));
- as->uid = cred->uid;
- as->euid = cred->euid;
+ as->cred = get_current_cred();
security_task_getsecid(current, &as->secid);
if (!is_in && uurb->buffer_length > 0) {
if (copy_from_user(as->urb->transfer_buffer, uurb->buffer,
@@ -1983,9 +1980,8 @@ static void usbdev_remove(struct usb_device *udev)
sinfo.si_errno = EPIPE;
sinfo.si_code = SI_ASYNCIO;
sinfo.si_addr = ps->disccontext;
- kill_pid_info_as_uid(ps->discsignr, &sinfo,
- ps->disc_pid, ps->disc_uid,
- ps->disc_euid, ps->secid);
+ kill_pid_info_as_cred(ps->discsignr, &sinfo,
+ ps->disc_pid, ps->cred, ps->secid);
}
}
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4ac2c05..57ddb52 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2166,7 +2166,8 @@ extern int force_sigsegv(int, struct task_struct *);
extern int force_sig_info(int, struct siginfo *, struct task_struct *);
extern int __kill_pgrp_info(int sig, struct siginfo *info, struct pid *pgrp);
extern int kill_pid_info(int sig, struct siginfo *info, struct pid *pid);
-extern int kill_pid_info_as_uid(int, struct siginfo *, struct pid *, uid_t, uid_t, u32);
+extern int kill_pid_info_as_cred(int, struct siginfo *, struct pid *,
+ const struct cred *, u32);
extern int kill_pgrp(struct pid *pid, int sig, int priv);
extern int kill_pid(struct pid *pid, int sig, int priv);
extern int kill_proc_info(int, struct siginfo *, pid_t);
diff --git a/kernel/signal.c b/kernel/signal.c
index 291c970..d252be2 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1344,13 +1344,24 @@ int kill_proc_info(int sig, struct siginfo *info, pid_t pid)
return error;
}

+static int kill_as_cred_perm(const struct cred *cred,
+ struct task_struct *target)
+{
+ const struct cred *pcred = __task_cred(target);
+ if (cred->user_ns != pcred->user_ns)
+ return 0;
+ if (cred->euid != pcred->suid && cred->euid != pcred->uid &&
+ cred->uid != pcred->suid && cred->uid != pcred->uid)
+ return 0;
+ return 1;
+}
+
/* like kill_pid_info(), but doesn't use uid/euid of "current" */
-int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
- uid_t uid, uid_t euid, u32 secid)
+int kill_pid_info_as_cred(int sig, struct siginfo *info, struct pid *pid,
+ const struct cred *cred, u32 secid)
{
int ret = -EINVAL;
struct task_struct *p;
- const struct cred *pcred;
unsigned long flags;

if (!valid_signal(sig))
@@ -1362,10 +1373,7 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
ret = -ESRCH;
goto out_unlock;
}
- pcred = __task_cred(p);
- if (si_fromuser(info) &&
- euid != pcred->suid && euid != pcred->uid &&
- uid != pcred->suid && uid != pcred->uid) {
+ if (si_fromuser(info) && !kill_as_cred_perm(cred, p)) {
ret = -EPERM;
goto out_unlock;
}
@@ -1384,7 +1392,7 @@ out_unlock:
rcu_read_unlock();
return ret;
}
-EXPORT_SYMBOL_GPL(kill_pid_info_as_uid);
+EXPORT_SYMBOL_GPL(kill_pid_info_as_cred);

/*
* kill_something_info() interprets pid in interesting ways just like kill(2).
--
1.7.0.4

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