Messages in this thread Patch in this message | | | From | Duoming Zhou <> | Subject | [PATCH V3] ax25: Fix refcount leaks caused by ax25_cb_del() | Date | Fri, 11 Mar 2022 09:46:24 +0800 |
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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@osterried.de> Signed-off-by: Duoming Zhou <duoming@zju.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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