From: Ondrej Kozina Date: Tue, 31 Jan 2017 14:47:11 +0000 (+0100) Subject: dm crypt: replace RCU read-side section with rwsem X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f5b0cba8f23915e92932f11eb063e37d70556a89;p=linux-beck.git dm crypt: replace RCU read-side section with rwsem The lockdep splat below hints at a bug in RCU usage in dm-crypt that was introduced with commit c538f6ec9f56 ("dm crypt: add ability to use keys from the kernel key retention service"). The kernel keyring function user_key_payload() is in fact a wrapper for rcu_dereference_protected() which must not be called with only rcu_read_lock() section mark. Unfortunately the kernel keyring subsystem doesn't currently provide an interface that allows the use of an RCU read-side section. So for now we must drop RCU in favour of rwsem until a proper function is made available in the kernel keyring subsystem. =============================== [ INFO: suspicious RCU usage. ] 4.10.0-rc5 #2 Not tainted ------------------------------- ./include/keys/user-type.h:53 suspicious rcu_dereference_protected() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 2 locks held by cryptsetup/6464: #0: (&md->type_lock){+.+.+.}, at: [] dm_lock_md_type+0x12/0x20 [dm_mod] #1: (rcu_read_lock){......}, at: [] crypt_set_key+0x1d8/0x4b0 [dm_crypt] stack backtrace: CPU: 1 PID: 6464 Comm: cryptsetup Not tainted 4.10.0-rc5 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 04/01/2014 Call Trace: dump_stack+0x67/0x92 lockdep_rcu_suspicious+0xc5/0x100 crypt_set_key+0x351/0x4b0 [dm_crypt] ? crypt_set_key+0x1d8/0x4b0 [dm_crypt] crypt_ctr+0x341/0xa53 [dm_crypt] dm_table_add_target+0x147/0x330 [dm_mod] table_load+0x111/0x350 [dm_mod] ? retrieve_status+0x1c0/0x1c0 [dm_mod] ctl_ioctl+0x1f5/0x510 [dm_mod] dm_ctl_ioctl+0xe/0x20 [dm_mod] do_vfs_ioctl+0x8e/0x690 ? ____fput+0x9/0x10 ? task_work_run+0x7e/0xa0 ? trace_hardirqs_on_caller+0x122/0x1b0 SyS_ioctl+0x3c/0x70 entry_SYSCALL_64_fastpath+0x18/0xad RIP: 0033:0x7f392c9a4ec7 RSP: 002b:00007ffef6383378 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007ffef63830a0 RCX: 00007f392c9a4ec7 RDX: 000000000124fcc0 RSI: 00000000c138fd09 RDI: 0000000000000005 RBP: 00007ffef6383090 R08: 00000000ffffffff R09: 00000000012482b0 R10: 2a28205d34383336 R11: 0000000000000246 R12: 00007f392d803a08 R13: 00007ffef63831e0 R14: 0000000000000000 R15: 00007f392d803a0b Fixes: c538f6ec9f56 ("dm crypt: add ability to use keys from the kernel key retention service") Reported-by: Milan Broz Signed-off-by: Ondrej Kozina Reviewed-by: Mikulas Patocka Signed-off-by: Mike Snitzer --- diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c index 7c6c57216bf2..8a9f742d8ed7 100644 --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -1534,18 +1534,18 @@ static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_string return PTR_ERR(key); } - rcu_read_lock(); + down_read(&key->sem); ukp = user_key_payload(key); if (!ukp) { - rcu_read_unlock(); + up_read(&key->sem); key_put(key); kzfree(new_key_string); return -EKEYREVOKED; } if (cc->key_size != ukp->datalen) { - rcu_read_unlock(); + up_read(&key->sem); key_put(key); kzfree(new_key_string); return -EINVAL; @@ -1553,7 +1553,7 @@ static int crypt_set_keyring_key(struct crypt_config *cc, const char *key_string memcpy(cc->key, ukp->data, cc->key_size); - rcu_read_unlock(); + up_read(&key->sem); key_put(key); /* clear the flag since following operations may invalidate previously valid key */