CVE-2014-2672: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (CWE-362)
value: Race condition in the ath_tx_aggr_sleep function in drivers/net/wireless/ath/ath9k/xmit.c in the Linux kernel before 3.13.7 allows remote attackers to cause a denial of service (system crash) via a large amount of network traffic that triggers certain list deletions.
CWE description: The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.
Published: 2014-04-01T06:35Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: drivers/net/wireless/ath/ath9k/xmit.c
Commit date: 2014-02-20 15:53:20 -0500
Commit message: ath9k: protect tid->sched check

We check tid->sched without a lock taken on ath_tx_aggr_sleep(). That
is race condition which can result of doing list_del(&tid->list) twice
(second time with poisoned list node) and cause crash like shown below:

[424271.637220] BUG: unable to handle kernel paging request at 00100104
[424271.637328] IP: [<f90fc072>] ath_tx_aggr_sleep+0x62/0xe0 [ath9k]
...
[424271.639953] Call Trace:
[424271.639998]  [<f90f6900>] ? ath9k_get_survey+0x110/0x110 [ath9k]
[424271.640083]  [<f90f6942>] ath9k_sta_notify+0x42/0x50 [ath9k]
[424271.640177]  [<f809cfef>] sta_ps_start+0x8f/0x1c0 [mac80211]
[424271.640258]  [<c10f730e>] ? free_compound_page+0x2e/0x40
[424271.640346]  [<f809e915>] ieee80211_rx_handlers+0x9d5/0x2340 [mac80211]
[424271.640437]  [<c112f048>] ? kmem_cache_free+0x1d8/0x1f0
[424271.640510]  [<c1345a84>] ? kfree_skbmem+0x34/0x90
[424271.640578]  [<c10fc23c>] ? put_page+0x2c/0x40
[424271.640640]  [<c1345a84>] ? kfree_skbmem+0x34/0x90
[424271.640706]  [<c1345a84>] ? kfree_skbmem+0x34/0x90
[424271.640787]  [<f809dde3>] ? ieee80211_rx_handlers_result+0x73/0x1d0 [mac80211]
[424271.640897]  [<f80a07a0>] ieee80211_prepare_and_rx_handle+0x520/0xad0 [mac80211]
[424271.641009]  [<f809e22d>] ? ieee80211_rx_handlers+0x2ed/0x2340 [mac80211]
[424271.641104]  [<c13846ce>] ? ip_output+0x7e/0xd0
[424271.641182]  [<f80a1057>] ieee80211_rx+0x307/0x7c0 [mac80211]
[424271.641266]  [<f90fa6ee>] ath_rx_tasklet+0x88e/0xf70 [ath9k]
[424271.641358]  [<f80a0f2c>] ? ieee80211_rx+0x1dc/0x7c0 [mac80211]
[424271.641445]  [<f90f82db>] ath9k_tasklet+0xcb/0x130 [ath9k]

Bug report:
https://bugzilla.kernel.org/show_bug.cgi?id=70551

Reported-and-tested-by: Max Sydorenko <maxim.stargazer@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

Diff: diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 0a75e2f68c9dc3..4f4ce83f7ab4af 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -1442,18 +1442,20 @@ void ath_tx_aggr_sleep(struct ieee80211_sta *sta, struct ath_softc *sc,
 	int tidno;
 
 	for (tidno = 0, tid = &an->tid[tidno];
 	     tidno < IEEE80211_NUM_TIDS; tidno++, tid++) {
 
-		if (!tid->sched)
-			continue;
-
 		ac = tid->ac;
 		txq = ac->txq;
 
 		ath_txq_lock(sc, txq);
 
+		if (!tid->sched) {
+			ath_txq_unlock(sc, txq);
+			continue;
+		}
+
 		buffered = ath_tid_has_buffered(tid);
 
 		tid->sched = false;
 		list_del(&tid->list);
 

Vulnerable code: 		if (!tid->sched)
			continue;

Fixed code: 		if (!tid->sched) {
			ath_txq_unlock(sc, txq);
			continue;
		}