From 749329594b5e0fb612b2de642a692323ddf661dd Mon Sep 17 00:00:00 2001 From: Bob Copeland Date: Fri, 18 Mar 2016 22:03:24 -0400 Subject: [PATCH] mac80211: mesh: fix crash in mesh_path_timer The mesh_path_reclaim() function, called from an rcu callback, cancels the mesh_path_timer associated with a mesh path. Unfortunately, this call can happen much later, perhaps after the hash table itself is destroyed. Such a situation led to the following crash in mesh_path_send_to_gates() when dereferencing the tbl pointer: [ 23.901661] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [ 23.905516] IP: [] mesh_path_send_to_gates+0x2b/0x740 [ 23.908757] PGD 99ca067 PUD 99c4067 PMD 0 [ 23.910789] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [ 23.913485] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.5.0-rc6-wt+ #43 [ 23.916675] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014 [ 23.920471] task: ffffffff81685500 ti: ffffffff81678000 task.ti: ffffffff81678000 [ 23.922619] RIP: 0010:[] [] mesh_path_send_to_gates+0x2b/0x740 [ 23.925237] RSP: 0018:ffff88000b403d30 EFLAGS: 00010286 [ 23.926739] RAX: 0000000000000000 RBX: ffff880009bc0d20 RCX: 0000000000000102 [ 23.928796] RDX: 000000000000002e RSI: 0000000000000001 RDI: ffff880009bc0d20 [ 23.930895] RBP: ffff88000b403e18 R08: 0000000000000001 R09: 0000000000000001 [ 23.932917] R10: 0000000000000000 R11: 0000000000000001 R12: ffff880009c20940 [ 23.936370] R13: ffff880009bc0e70 R14: ffff880009c21c40 R15: ffff880009bc0d20 [ 23.939823] FS: 0000000000000000(0000) GS:ffff88000b400000(0000) knlGS:0000000000000000 [ 23.943688] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 23.946429] CR2: 0000000000000008 CR3: 00000000099c5000 CR4: 00000000000006b0 [ 23.949861] Stack: [ 23.950840] 000000000000002e ffff880009c20940 ffff88000b403da8 ffffffff8109e551 [ 23.954467] ffffffff82711be2 000000000000002e 0000000000000000 ffffffff8166a5f5 [ 23.958141] 0000000000685ce8 0000000000000246 ffff880009bc0d20 ffff880009c20940 [ 23.961801] Call Trace: [ 23.962987] [ 23.963963] [] ? vprintk_emit+0x351/0x5e0 [ 23.966782] [] ? vprintk_default+0x1f/0x30 [ 23.969529] [] ? printk+0x48/0x50 [ 23.971956] [] mesh_path_timer+0x133/0x160 [ 23.974707] [] ? mesh_nexthop_resolve+0x230/0x230 [ 23.977775] [] call_timer_fn+0xce/0x330 [ 23.980448] [] ? call_timer_fn+0x5/0x330 [ 23.983126] [] ? mesh_nexthop_resolve+0x230/0x230 [ 23.986091] [] run_timer_softirq+0x22c/0x390 Instead of cancelling in the RCU callback, set a new flag to prevent the timer from being rearmed, and then cancel the timer synchronously when freeing the mesh path. This leaves mesh_path_reclaim() doing nothing but kfree, so switch to kfree_rcu(). Fixes: 3b302ada7f0a ("mac80211: mesh: move path tables into if_mesh") Signed-off-by: Bob Copeland Signed-off-by: Johannes Berg --- net/mac80211/mesh.h | 3 +++ net/mac80211/mesh_hwmp.c | 4 ++++ net/mac80211/mesh_pathtbl.c | 33 ++++++++++++++++++--------------- 3 files changed, 25 insertions(+), 15 deletions(-) diff --git a/net/mac80211/mesh.h b/net/mac80211/mesh.h index cc6854db156e..e1415c952e9c 100644 --- a/net/mac80211/mesh.h +++ b/net/mac80211/mesh.h @@ -32,6 +32,8 @@ * @MESH_PATH_RESOLVED: the mesh path can has been resolved * @MESH_PATH_REQ_QUEUED: there is an unsent path request for this destination * already queued up, waiting for the discovery process to start. + * @MESH_PATH_DELETED: the mesh path has been deleted and should no longer + * be used * * MESH_PATH_RESOLVED is used by the mesh path timer to * decide when to stop or cancel the mesh path discovery. @@ -43,6 +45,7 @@ enum mesh_path_flags { MESH_PATH_FIXED = BIT(3), MESH_PATH_RESOLVED = BIT(4), MESH_PATH_REQ_QUEUED = BIT(5), + MESH_PATH_DELETED = BIT(6), }; /** diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c index 5b6aec1a0630..2748cf627ee3 100644 --- a/net/mac80211/mesh_hwmp.c +++ b/net/mac80211/mesh_hwmp.c @@ -1012,6 +1012,10 @@ void mesh_path_start_discovery(struct ieee80211_sub_if_data *sdata) goto enddiscovery; spin_lock_bh(&mpath->state_lock); + if (mpath->flags & MESH_PATH_DELETED) { + spin_unlock_bh(&mpath->state_lock); + goto enddiscovery; + } mpath->flags &= ~MESH_PATH_REQ_QUEUED; if (preq_node->flags & PREQ_Q_F_START) { if (mpath->flags & MESH_PATH_RESOLVING) { diff --git a/net/mac80211/mesh_pathtbl.c b/net/mac80211/mesh_pathtbl.c index 7455397f8c3b..1c9412a29ca3 100644 --- a/net/mac80211/mesh_pathtbl.c +++ b/net/mac80211/mesh_pathtbl.c @@ -18,6 +18,8 @@ #include "ieee80211_i.h" #include "mesh.h" +static void mesh_path_free_rcu(struct mesh_table *tbl, struct mesh_path *mpath); + static u32 mesh_table_hash(const void *addr, u32 len, u32 seed) { /* Use last four bytes of hw addr as hash index */ @@ -40,18 +42,12 @@ static inline bool mpath_expired(struct mesh_path *mpath) !(mpath->flags & MESH_PATH_FIXED); } -static void mesh_path_reclaim(struct rcu_head *rp) -{ - struct mesh_path *mpath = container_of(rp, struct mesh_path, rcu); - - del_timer_sync(&mpath->timer); - kfree(mpath); -} - -static void mesh_path_rht_free(void *ptr, void *unused_arg) +static void mesh_path_rht_free(void *ptr, void *tblptr) { struct mesh_path *mpath = ptr; - call_rcu(&mpath->rcu, mesh_path_reclaim); + struct mesh_table *tbl = tblptr; + + mesh_path_free_rcu(tbl, mpath); } static struct mesh_table *mesh_table_alloc(void) @@ -77,7 +73,7 @@ static struct mesh_table *mesh_table_alloc(void) static void mesh_table_free(struct mesh_table *tbl) { rhashtable_free_and_destroy(&tbl->rhead, - mesh_path_rht_free, NULL); + mesh_path_rht_free, tbl); kfree(tbl); } @@ -551,18 +547,25 @@ void mesh_plink_broken(struct sta_info *sta) rhashtable_walk_exit(&iter); } -static void __mesh_path_del(struct mesh_table *tbl, struct mesh_path *mpath) +static void mesh_path_free_rcu(struct mesh_table *tbl, + struct mesh_path *mpath) { struct ieee80211_sub_if_data *sdata = mpath->sdata; - rhashtable_remove_fast(&tbl->rhead, &mpath->rhash, mesh_rht_params); spin_lock_bh(&mpath->state_lock); - mpath->flags |= MESH_PATH_RESOLVING; + mpath->flags |= MESH_PATH_RESOLVING | MESH_PATH_DELETED; mesh_gate_del(tbl, mpath); - call_rcu(&mpath->rcu, mesh_path_reclaim); spin_unlock_bh(&mpath->state_lock); + del_timer_sync(&mpath->timer); atomic_dec(&sdata->u.mesh.mpaths); atomic_dec(&tbl->entries); + kfree_rcu(mpath, rcu); +} + +static void __mesh_path_del(struct mesh_table *tbl, struct mesh_path *mpath) +{ + rhashtable_remove_fast(&tbl->rhead, &mpath->rhash, mesh_rht_params); + mesh_path_free_rcu(tbl, mpath); } /**