Re: [PATCH] net/sctp: always initialise sctp_ht_iter::start_fail
From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: 2016-07-23 13:39:35
Also in:
linux-sctp, stable
On Sat, Jul 23, 2016 at 11:52:23AM +0200, Vegard Nossum wrote:
seq_read() can call ->start() twice on the same iterator more than once (e.g. once through traverse() and once in seq_read() itself).
But when traverse() returns the error, it goes to Done label, skipping the call to ->start() from seq_read(), or am I missing something? Though yes, if sctp_ht_iter memory is actually re-used without initializting between seq_read()s, it triggers the issue you described. How did you trigger this, reading after an error on the file descriptor?
quoted hunk ↗ jump to hunk
We should initialize sctp_ht_iter::start_fail to zero if ->start() succeeds, otherwise it's possible that we leave an old value of 1 there, which will cause ->stop() to not call sctp_transport_walk_stop(), which causes all sorts of problems like not calling rcu_read_unlock() (and preempt_enable()), eventually leading to more warnings like this: BUG: sleeping function called from invalid context at mm/slab.h:388 in_atomic(): 0, irqs_disabled(): 0, pid: 16551, name: trinity-c2 Preemption disabled at:[<ffffffff819bceb6>] rhashtable_walk_start+0x46/0x150 [<ffffffff81149abb>] preempt_count_add+0x1fb/0x280 [<ffffffff83295892>] _raw_spin_lock+0x12/0x40 [<ffffffff819bceb6>] rhashtable_walk_start+0x46/0x150 [<ffffffff82ec665f>] sctp_transport_walk_start+0x2f/0x60 [<ffffffff82edda1d>] sctp_transport_seq_start+0x4d/0x150 [<ffffffff81439e50>] traverse+0x170/0x850 [<ffffffff8143aeec>] seq_read+0x7cc/0x1180 [<ffffffff814f996c>] proc_reg_read+0xbc/0x180 [<ffffffff813d0384>] do_loop_readv_writev+0x134/0x210 [<ffffffff813d2a95>] do_readv_writev+0x565/0x660 [<ffffffff813d6857>] vfs_readv+0x67/0xa0 [<ffffffff813d6c16>] do_preadv+0x126/0x170 [<ffffffff813d710c>] SyS_preadv+0xc/0x10 [<ffffffff8100334c>] do_syscall_64+0x19c/0x410 [<ffffffff83296225>] return_from_SYSCALL_64+0x0/0x6a [<ffffffffffffffff>] 0xffffffffffffffff (Notice that this is a subtly different stacktrace from the previous bug I reported.) Cc: Xin Long <lucien.xin@gmail.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: Eric W. Biederman <redacted> Cc: stable@vger.kernel.org Signed-off-by: Vegard Nossum <redacted> --- net/sctp/proc.c | 1 + 1 file changed, 1 insertion(+)diff --git a/net/sctp/proc.c b/net/sctp/proc.c index 4cb5aed..ef8ba77 100644 --- a/net/sctp/proc.c +++ b/net/sctp/proc.c@@ -293,6 +293,7 @@ static void *sctp_transport_seq_start(struct seq_file *seq, loff_t *pos) return ERR_PTR(err); } + iter->start_fail = 0; return sctp_transport_get_idx(seq_file_net(seq), &iter->hti, *pos); }-- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html