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Message-Id: <20220311014624.51117-1-duoming@zju.edu.cn>
Date: Fri, 11 Mar 2022 09:46:24 +0800
From: Duoming Zhou <duoming@....edu.cn>
To: linux-hams@...r.kernel.org
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
jreuter@...na.de, kuba@...nel.org, davem@...emloft.net,
ralf@...ux-mips.org, thomas@...erried.de,
Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH V3] ax25: Fix refcount leaks caused by ax25_cb_del()
The previous commit d01ffb9eee4a ("ax25: add refcount in ax25_dev to
avoid UAF bugs") and commit feef318c855a ("ax25: fix UAF bugs of
net_device caused by rebinding operation") increase the refcounts of
ax25_dev and net_device in ax25_bind() and decrease the matching refcounts
in ax25_kill_by_device() in order to prevent UAF bugs, but there are
reference count leaks.
The root cause of refcount leaks is shown below:
(Thread 1) | (Thread 2)
ax25_bind() |
... |
ax25_addr_ax25dev() |
ax25_dev_hold() //(1) |
... |
dev_hold_track() //(2) |
... | ax25_destroy_socket()
| ax25_cb_del()
| ...
| hlist_del_init() //(3)
|
|
(thread 3) |
ax25_kill_by_device() |
... |
ax25_for_each(s, &ax25_list) { |
if (s->ax25_dev == ax25_dev) //(4) |
... |
Firstly, we use ax25_bind() to increase the refcount of ax25_dev in
position (1) and increase the refcount of net_device in position (2).
Then, we use ax25_cb_del() invoked by ax25_destroy_socket() to delete
ax25_cb in hlist in position (3) before calling ax25_kill_by_device().
Finally, the decrements of refcounts in ax25_kill_by_device() will not
be executed, because no s->ax25_dev equals to ax25_dev in position (4).
This patch adds a flag in ax25_dev in order to prevent reference count
leaks. If the above condition happens, the "test_bit" condition check
in ax25_kill_by_device() could pass and the refcounts could be
decreased properly.
Fixes: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
Fixes: feef318c855a ("ax25: fix UAF bugs of net_device caused by rebinding operation")
Reported-by: Thomas Osterried <thomas@...erried.de>
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
Changes in V3:
- Use one flag in ax25_dev to check.
- Make commit message more clearer.
- Fix format problem.
include/net/ax25.h | 5 +++++
net/ax25/af_ax25.c | 6 ++++++
net/ax25/ax25_dev.c | 1 +
3 files changed, 12 insertions(+)
diff --git a/include/net/ax25.h b/include/net/ax25.h
index 8221af1811d..ea6ca385190 100644
--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -158,6 +158,10 @@ enum {
#define AX25_DEF_PROTOCOL AX25_PROTO_STD_SIMPLEX /* Standard AX.25 */
#define AX25_DEF_DS_TIMEOUT 180000 /* DAMA timeout 3 minutes */
+#define AX25_DEV_INIT 0
+#define AX25_DEV_KILL 0
+#define AX25_DEV_BIND 1
+
typedef struct ax25_uid_assoc {
struct hlist_node uid_node;
refcount_t refcount;
@@ -240,6 +244,7 @@ typedef struct ax25_dev {
ax25_dama_info dama;
#endif
refcount_t refcount;
+ unsigned long flag;
} ax25_dev;
typedef struct ax25_cb {
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 6bd09718077..fc564b87acc 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -86,6 +86,7 @@ static void ax25_kill_by_device(struct net_device *dev)
again:
ax25_for_each(s, &ax25_list) {
if (s->ax25_dev == ax25_dev) {
+ set_bit(AX25_DEV_KILL, &ax25_dev->flag);
sk = s->sk;
if (!sk) {
spin_unlock_bh(&ax25_list_lock);
@@ -115,6 +116,10 @@ static void ax25_kill_by_device(struct net_device *dev)
}
}
spin_unlock_bh(&ax25_list_lock);
+ if (!test_bit(AX25_DEV_KILL, &ax25_dev->flag) && test_bit(AX25_DEV_BIND, &ax25_dev->flag)) {
+ dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
+ ax25_dev_put(ax25_dev);
+ }
}
/*
@@ -1132,6 +1137,7 @@ static int ax25_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
done:
ax25_cb_add(ax25);
sock_reset_flag(sk, SOCK_ZAPPED);
+ set_bit(AX25_DEV_BIND, &ax25_dev->flag);
out:
release_sock(sk);
diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index d2a244e1c26..9b04d74a1be 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -77,6 +77,7 @@ void ax25_dev_device_up(struct net_device *dev)
ax25_dev->values[AX25_VALUES_PACLEN] = AX25_DEF_PACLEN;
ax25_dev->values[AX25_VALUES_PROTOCOL] = AX25_DEF_PROTOCOL;
ax25_dev->values[AX25_VALUES_DS_TIMEOUT]= AX25_DEF_DS_TIMEOUT;
+ ax25_dev->flag = AX25_DEV_INIT;
#if defined(CONFIG_AX25_DAMA_SLAVE) || defined(CONFIG_AX25_DAMA_MASTER)
ax25_ds_setup_timer(ax25_dev);
--
2.17.1
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