From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
stable@vger.kernel.org, stable@kernel.org,
Jann Horn <jannh@google.com>, Jiri Slaby <jirislaby@kernel.org>
Subject: [PATCH 4.4 25/39] tty: Fix ->session locking
Date: Thu, 10 Dec 2020 15:26:36 +0100 [thread overview]
Message-ID: <20201210142602.139036502@linuxfoundation.org> (raw)
In-Reply-To: <20201210142600.887734129@linuxfoundation.org>
From: Jann Horn <jannh@google.com>
commit c8bcd9c5be24fb9e6132e97da5a35e55a83e36b9 upstream.
Currently, locking of ->session is very inconsistent; most places
protect it using the legacy tty mutex, but disassociate_ctty(),
__do_SAK(), tiocspgrp() and tiocgsid() don't.
Two of the writers hold the ctrl_lock (because they already need it for
->pgrp), but __proc_set_tty() doesn't do that yet.
On a PREEMPT=y system, an unprivileged user can theoretically abuse
this broken locking to read 4 bytes of freed memory via TIOCGSID if
tiocgsid() is preempted long enough at the right point. (Other things
might also go wrong, especially if root-only ioctls are involved; I'm
not sure about that.)
Change the locking on ->session such that:
- tty_lock() is held by all writers: By making disassociate_ctty()
hold it. This should be fine because the same lock can already be
taken through the call to tty_vhangup_session().
The tricky part is that we need to shorten the area covered by
siglock to be able to take tty_lock() without ugly retry logic; as
far as I can tell, this should be fine, since nothing in the
signal_struct is touched in the `if (tty)` branch.
- ctrl_lock is held by all writers: By changing __proc_set_tty() to
hold the lock a little longer.
- All readers that aren't holding tty_lock() hold ctrl_lock: By
adding locking to tiocgsid() and __do_SAK(), and expanding the area
covered by ctrl_lock in tiocspgrp().
Cc: stable@kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/tty_io.c | 51 +++++++++++++++++++++++++++++++++++++--------------
include/linux/tty.h | 4 ++++
2 files changed, 41 insertions(+), 14 deletions(-)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -537,8 +537,8 @@ static void __proc_set_tty(struct tty_st
put_pid(tty->session);
put_pid(tty->pgrp);
tty->pgrp = get_pid(task_pgrp(current));
- spin_unlock_irqrestore(&tty->ctrl_lock, flags);
tty->session = get_pid(task_session(current));
+ spin_unlock_irqrestore(&tty->ctrl_lock, flags);
if (current->signal->tty) {
tty_debug(tty, "current tty %s not NULL!!\n",
current->signal->tty->name);
@@ -929,21 +929,24 @@ void disassociate_ctty(int on_exit)
spin_lock_irq(¤t->sighand->siglock);
put_pid(current->signal->tty_old_pgrp);
current->signal->tty_old_pgrp = NULL;
-
tty = tty_kref_get(current->signal->tty);
+ spin_unlock_irq(¤t->sighand->siglock);
+
if (tty) {
unsigned long flags;
+
+ tty_lock(tty);
spin_lock_irqsave(&tty->ctrl_lock, flags);
put_pid(tty->session);
put_pid(tty->pgrp);
tty->session = NULL;
tty->pgrp = NULL;
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
+ tty_unlock(tty);
tty_kref_put(tty);
} else
tty_debug_hangup(tty, "no current tty\n");
- spin_unlock_irq(¤t->sighand->siglock);
/* Now clear signal->tty under the lock */
read_lock(&tasklist_lock);
session_clear_tty(task_session(current));
@@ -2601,14 +2604,19 @@ static int tiocspgrp(struct tty_struct *
return -ENOTTY;
if (retval)
return retval;
- if (!current->signal->tty ||
- (current->signal->tty != real_tty) ||
- (real_tty->session != task_session(current)))
- return -ENOTTY;
+
if (get_user(pgrp_nr, p))
return -EFAULT;
if (pgrp_nr < 0)
return -EINVAL;
+
+ spin_lock_irq(&real_tty->ctrl_lock);
+ if (!current->signal->tty ||
+ (current->signal->tty != real_tty) ||
+ (real_tty->session != task_session(current))) {
+ retval = -ENOTTY;
+ goto out_unlock_ctrl;
+ }
rcu_read_lock();
pgrp = find_vpid(pgrp_nr);
retval = -ESRCH;
@@ -2618,12 +2626,12 @@ static int tiocspgrp(struct tty_struct *
if (session_of_pgrp(pgrp) != task_session(current))
goto out_unlock;
retval = 0;
- spin_lock_irq(&real_tty->ctrl_lock);
put_pid(real_tty->pgrp);
real_tty->pgrp = get_pid(pgrp);
- spin_unlock_irq(&real_tty->ctrl_lock);
out_unlock:
rcu_read_unlock();
+out_unlock_ctrl:
+ spin_unlock_irq(&real_tty->ctrl_lock);
return retval;
}
@@ -2635,21 +2643,31 @@ out_unlock:
*
* Obtain the session id of the tty. If there is no session
* return an error.
- *
- * Locking: none. Reference to current->signal->tty is safe.
*/
static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t __user *p)
{
+ unsigned long flags;
+ pid_t sid;
+
/*
* (tty == real_tty) is a cheap way of
* testing if the tty is NOT a master pty.
*/
if (tty == real_tty && current->signal->tty != real_tty)
return -ENOTTY;
+
+ spin_lock_irqsave(&real_tty->ctrl_lock, flags);
if (!real_tty->session)
- return -ENOTTY;
- return put_user(pid_vnr(real_tty->session), p);
+ goto err;
+ sid = pid_vnr(real_tty->session);
+ spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
+
+ return put_user(sid, p);
+
+err:
+ spin_unlock_irqrestore(&real_tty->ctrl_lock, flags);
+ return -ENOTTY;
}
/**
@@ -3061,10 +3079,14 @@ void __do_SAK(struct tty_struct *tty)
struct task_struct *g, *p;
struct pid *session;
int i;
+ unsigned long flags;
if (!tty)
return;
- session = tty->session;
+
+ spin_lock_irqsave(&tty->ctrl_lock, flags);
+ session = get_pid(tty->session);
+ spin_unlock_irqrestore(&tty->ctrl_lock, flags);
tty_ldisc_flush(tty);
@@ -3100,6 +3122,7 @@ void __do_SAK(struct tty_struct *tty)
task_unlock(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
+ put_pid(session);
#endif
}
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -280,6 +280,10 @@ struct tty_struct {
struct termiox *termiox; /* May be NULL for unsupported */
char name[64];
struct pid *pgrp; /* Protected by ctrl lock */
+ /*
+ * Writes protected by both ctrl lock and legacy mutex, readers must use
+ * at least one of them.
+ */
struct pid *session;
unsigned long flags;
int count;
next prev parent reply other threads:[~2020-12-10 19:27 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-10 14:26 [PATCH 4.4 00/39] 4.4.248-rc1 review Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 01/39] net/af_iucv: set correct sk_protocol for child sockets Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 02/39] rose: Fix Null pointer dereference in rose_send_frame() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 03/39] usbnet: ipheth: fix connectivity with iOS 14 Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 04/39] bonding: wait for sysfs kobject destruction before freeing struct slave Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 05/39] netfilter: bridge: reset skb->pkt_type after NF_INET_POST_ROUTING traversal Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 06/39] net/x25: prevent a couple of overflows Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 07/39] cxgb3: fix error return code in t3_sge_alloc_qset() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 08/39] net: pasemi: fix error return code in pasemi_mac_open() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 09/39] dt-bindings: net: correct interrupt flags in examples Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 10/39] Input: xpad - support Ardwiino Controllers Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 11/39] Input: i8042 - add ByteSpeed touchpad to noloop table Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 12/39] powerpc: Stop exporting __clear_user which is now inlined Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 13/39] btrfs: sysfs: init devices outside of the chunk_mutex Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 14/39] vlan: consolidate VLAN parsing code and limit max parsing depth Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 15/39] geneve: pull IP header before ECN decapsulation Greg Kroah-Hartman
2020-12-10 14:32 ` Eric Dumazet
2020-12-10 14:38 ` Greg Kroah-Hartman
2020-12-10 14:40 ` Greg Kroah-Hartman
2020-12-10 14:53 ` Eric Dumazet
2020-12-10 15:36 ` Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 16/39] usb: gadget: f_fs: Use local copy of descriptors for userspace copy Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 17/39] USB: serial: kl5kusb105: fix memleak on open Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 18/39] USB: serial: ch341: add new Product ID for CH341A Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 19/39] USB: serial: ch341: sort device-id entries Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 20/39] USB: serial: option: add Fibocom NL668 variants Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 21/39] USB: serial: option: add support for Thales Cinterion EXS82 Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 22/39] tty: Fix ->pgrp locking in tiocspgrp() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 23/39] ALSA: hda/realtek - Add new codec supported for ALC897 Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 24/39] ALSA: hda/generic: Add option to enforce preferred_dacs pairs Greg Kroah-Hartman
2020-12-10 14:26 ` Greg Kroah-Hartman [this message]
2020-12-10 14:26 ` [PATCH 4.4 26/39] cifs: fix potential use-after-free in cifs_echo_request() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 27/39] i2c: imx: Fix reset of I2SR_IAL flag Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 28/39] i2c: imx: Check for I2SR_IAL after every byte Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 29/39] arm64: assembler: make adr_l work in modules under KASLR Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 30/39] iommu/amd: Set DTE[IntTabLen] to represent 512 IRTEs Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 31/39] spi: Introduce device-managed SPI controller allocation Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 32/39] spi: bcm2835: Fix use-after-free on unbind Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 33/39] spi: bcm2835: Release the DMA channel if probe fails after dma_init Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 34/39] tracing: Fix userstacktrace option for instances Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 35/39] btrfs: cleanup cow block on error Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 36/39] mm/userfaultfd: do not access vma->vm_mm after calling handle_userfault() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 37/39] gfs2: check for empty rgrp tree in gfs2_ri_update Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 38/39] Input: i8042 - fix error return code in i8042_setup_aux() Greg Kroah-Hartman
2020-12-10 14:26 ` [PATCH 4.4 39/39] x86/uprobes: Do not use prefixes.nbytes when looping over prefixes.bytes Greg Kroah-Hartman
2020-12-10 20:37 ` [PATCH 4.4 00/39] 4.4.248-rc1 review Pavel Machek
2020-12-10 21:24 ` Shuah Khan
2020-12-11 0:05 ` Guenter Roeck
2020-12-11 12:06 ` Naresh Kamboju
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