| Message ID | 147024345952.19927.3613766301915316442.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Aug 03, 2016 at 05:57:39PM +0100, David Howells wrote: > There's a race between cachefiles_mark_object_inactive() and > cachefiles_cull(): > > (1) cachefiles_cull() can't delete a backing file until the cache object > is marked inactive, but as soon as that's the case it's fair game. > > (2) cachefiles_mark_object_inactive() marks the object as being inactive > and *only then* reads the i_blocks on the backing inode - but > cachefiles_cull() might've managed to delete it by this point. > > Fix this by making sure cachefiles_mark_object_inactive() gets any data it > needs from the backing inode before deactivating the object. > > Without this, the following oops may occur: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000098 > IP: [<ffffffffa06c5cc1>] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles] > ... > CPU: 11 PID: 527 Comm: kworker/u64:4 Tainted: G I ------------ 3.10.0-470.el7.x86_64 #1 > Hardware name: Hewlett-Packard HP Z600 Workstation/0B54h, BIOS 786G4 v03.19 03/11/2011 > Workqueue: fscache_object fscache_object_work_func [fscache] > task: ffff880035edaf10 ti: ffff8800b77c0000 task.ti: ffff8800b77c0000 > RIP: 0010:[<ffffffffa06c5cc1>] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles] > RSP: 0018:ffff8800b77c3d70 EFLAGS: 00010246 > RAX: 0000000000000000 RBX: ffff8800bf6cc400 RCX: 0000000000000034 > RDX: 0000000000000000 RSI: ffff880090ffc710 RDI: ffff8800bf761ef8 > RBP: ffff8800b77c3d88 R08: 2000000000000000 R09: 0090ffc710000000 > R10: ff51005d2ff1c400 R11: 0000000000000000 R12: ffff880090ffc600 > R13: ffff8800bf6cc520 R14: ffff8800bf6cc400 R15: ffff8800bf6cc498 > FS: 0000000000000000(0000) GS:ffff8800bb8c0000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > CR2: 0000000000000098 CR3: 00000000019ba000 CR4: 00000000000007e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Stack: > ffff880090ffc600 ffff8800bf6cc400 ffff8800867df140 ffff8800b77c3db0 > ffffffffa06c48cb ffff880090ffc600 ffff880090ffc180 ffff880090ffc658 > ffff8800b77c3df0 ffffffffa085d846 ffff8800a96b8150 ffff880090ffc600 > Call Trace: > [<ffffffffa06c48cb>] cachefiles_drop_object+0x6b/0xf0 [cachefiles] > [<ffffffffa085d846>] fscache_drop_object+0xd6/0x1e0 [fscache] > [<ffffffffa085d615>] fscache_object_work_func+0xa5/0x200 [fscache] > [<ffffffff810a605b>] process_one_work+0x17b/0x470 > [<ffffffff810a6e96>] worker_thread+0x126/0x410 > [<ffffffff810a6d70>] ? rescuer_thread+0x460/0x460 > [<ffffffff810ae64f>] kthread+0xcf/0xe0 > [<ffffffff810ae580>] ? kthread_create_on_node+0x140/0x140 > [<ffffffff81695418>] ret_from_fork+0x58/0x90 > [<ffffffff810ae580>] ? kthread_create_on_node+0x140/0x140 > > The oopsing code shows: > > callq 0xffffffff810af6a0 <wake_up_bit> > mov 0xf8(%r12),%rax > mov 0x30(%rax),%rax > mov 0x98(%rax),%rax <---- oops here > lock add %rax,0x130(%rbx) > > where this is: > > d_backing_inode(object->dentry)->i_blocks > > Fixes: a5b3a80b899bda0f456f1246c4c5a1191ea01519 (CacheFiles: Provide read-and-reset release counters for cachefilesd) > Reported-by: Jianhong Yin <jiyin@redhat.com> > Signed-off-by: David Howells <dhowells@redhat.com> > Reviewed-by: Jeff Layton <jlayton@redhat.com> > Reviewed-by: Steve Dickson <steved@redhat.com> > cc: stable@vger.kernel.org Applied. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c index 4ae75006e73b..3f7c2cd41f8f 100644 --- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -263,6 +263,8 @@ requeue: void cachefiles_mark_object_inactive(struct cachefiles_cache *cache, struct cachefiles_object *object) { + blkcnt_t i_blocks = d_backing_inode(object->dentry)->i_blocks; + write_lock(&cache->active_lock); rb_erase(&object->active_node, &cache->active_nodes); clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags); @@ -273,8 +275,7 @@ void cachefiles_mark_object_inactive(struct cachefiles_cache *cache, /* This object can now be culled, so we need to let the daemon know * that there is something it can remove if it needs to. */ - atomic_long_add(d_backing_inode(object->dentry)->i_blocks, - &cache->b_released); + atomic_long_add(i_blocks, &cache->b_released); if (atomic_inc_return(&cache->f_released)) cachefiles_state_changed(cache); }
There's a race between cachefiles_mark_object_inactive() and cachefiles_cull(): (1) cachefiles_cull() can't delete a backing file until the cache object is marked inactive, but as soon as that's the case it's fair game. (2) cachefiles_mark_object_inactive() marks the object as being inactive and *only then* reads the i_blocks on the backing inode - but cachefiles_cull() might've managed to delete it by this point. Fix this by making sure cachefiles_mark_object_inactive() gets any data it needs from the backing inode before deactivating the object. Without this, the following oops may occur: BUG: unable to handle kernel NULL pointer dereference at 0000000000000098 IP: [<ffffffffa06c5cc1>] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles] ... CPU: 11 PID: 527 Comm: kworker/u64:4 Tainted: G I ------------ 3.10.0-470.el7.x86_64 #1 Hardware name: Hewlett-Packard HP Z600 Workstation/0B54h, BIOS 786G4 v03.19 03/11/2011 Workqueue: fscache_object fscache_object_work_func [fscache] task: ffff880035edaf10 ti: ffff8800b77c0000 task.ti: ffff8800b77c0000 RIP: 0010:[<ffffffffa06c5cc1>] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles] RSP: 0018:ffff8800b77c3d70 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff8800bf6cc400 RCX: 0000000000000034 RDX: 0000000000000000 RSI: ffff880090ffc710 RDI: ffff8800bf761ef8 RBP: ffff8800b77c3d88 R08: 2000000000000000 R09: 0090ffc710000000 R10: ff51005d2ff1c400 R11: 0000000000000000 R12: ffff880090ffc600 R13: ffff8800bf6cc520 R14: ffff8800bf6cc400 R15: ffff8800bf6cc498 FS: 0000000000000000(0000) GS:ffff8800bb8c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000098 CR3: 00000000019ba000 CR4: 00000000000007e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffff880090ffc600 ffff8800bf6cc400 ffff8800867df140 ffff8800b77c3db0 ffffffffa06c48cb ffff880090ffc600 ffff880090ffc180 ffff880090ffc658 ffff8800b77c3df0 ffffffffa085d846 ffff8800a96b8150 ffff880090ffc600 Call Trace: [<ffffffffa06c48cb>] cachefiles_drop_object+0x6b/0xf0 [cachefiles] [<ffffffffa085d846>] fscache_drop_object+0xd6/0x1e0 [fscache] [<ffffffffa085d615>] fscache_object_work_func+0xa5/0x200 [fscache] [<ffffffff810a605b>] process_one_work+0x17b/0x470 [<ffffffff810a6e96>] worker_thread+0x126/0x410 [<ffffffff810a6d70>] ? rescuer_thread+0x460/0x460 [<ffffffff810ae64f>] kthread+0xcf/0xe0 [<ffffffff810ae580>] ? kthread_create_on_node+0x140/0x140 [<ffffffff81695418>] ret_from_fork+0x58/0x90 [<ffffffff810ae580>] ? kthread_create_on_node+0x140/0x140 The oopsing code shows: callq 0xffffffff810af6a0 <wake_up_bit> mov 0xf8(%r12),%rax mov 0x30(%rax),%rax mov 0x98(%rax),%rax <---- oops here lock add %rax,0x130(%rbx) where this is: d_backing_inode(object->dentry)->i_blocks Fixes: a5b3a80b899bda0f456f1246c4c5a1191ea01519 (CacheFiles: Provide read-and-reset release counters for cachefilesd) Reported-by: Jianhong Yin <jiyin@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> cc: stable@vger.kernel.org --- fs/cachefiles/namei.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html