The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 76e43c8ccaa35c30d5df853013561145a0f750a5 Mon Sep 17 00:00:00 2001

From: Eric Biggers ebiggers@google.com Date: Sun, 8 Sep 2019 20:15:18 -0700 Subject: [PATCH] fuse: fix deadlock with aio poll and fuse_iqueue::waitq.lock

When IOCB_CMD_POLL is used on the FUSE device, aio_poll() disables IRQs and takes kioctx::ctx_lock, then fuse_iqueue::waitq.lock.

This may have to wait for fuse_iqueue::waitq.lock to be released by one of many places that take it with IRQs enabled. Since the IRQ handler may take kioctx::ctx_lock, lockdep reports that a deadlock is possible.

Fix it by protecting the state of struct fuse_iqueue with a separate spinlock, and only accessing fuse_iqueue::waitq using the versions of the waitqueue functions which do IRQ-safe locking internally.

Reproducer:

#include <fcntl.h> #include <stdio.h> #include <sys/mount.h> #include <sys/stat.h> #include <sys/syscall.h> #include <unistd.h> #include <linux/aio_abi.h>

int main() { char opts[128]; int fd = open("/dev/fuse", O_RDWR); aio_context_t ctx = 0; struct iocb cb = { .aio_lio_opcode = IOCB_CMD_POLL, .aio_fildes = fd }; struct iocb *cbp = &cb;

sprintf(opts, "fd=%d,rootmode=040000,user_id=0,group_id=0", fd); mkdir("mnt", 0700); mount("foo", "mnt", "fuse", 0, opts); syscall(__NR_io_setup, 1, &ctx); syscall(__NR_io_submit, ctx, 1, &cbp); }

Beginning of lockdep output:

===================================================== WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected 5.3.0-rc5 #9 Not tainted ----------------------------------------------------- syz_fuse/135 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: 000000003590ceda (&fiq->waitq){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline] 000000003590ceda (&fiq->waitq){+.+.}, at: aio_poll fs/aio.c:1751 [inline] 000000003590ceda (&fiq->waitq){+.+.}, at: __io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825

and this task is already holding: 0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq include/linux/spinlock.h:363 [inline] 0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll fs/aio.c:1749 [inline] 0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one.constprop.0+0x1f4/0x5b0 fs/aio.c:1825 which would create a new lock dependency: (&(&ctx->ctx_lock)->rlock){..-.} -> (&fiq->waitq){+.+.}

but this new dependency connects a SOFTIRQ-irq-safe lock: (&(&ctx->ctx_lock)->rlock){..-.}

[...]

Reported-by: syzbot+af05535bb79520f95431@syzkaller.appspotmail.com Reported-by: syzbot+d86c4426a01f60feddc7@syzkaller.appspotmail.com Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL") Cc: stable@vger.kernel.org # v4.19+ Cc: Christoph Hellwig hch@lst.de Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index fdb85895737b..5a5dd6b2f91e 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -377,7 +377,7 @@ static void queue_request(struct fuse_iqueue *fiq, struct fuse_req *req) req->in.h.len = sizeof(struct fuse_in_header) + len_args(req->in.numargs, (struct fuse_arg *) req->in.args); list_add_tail(&req->list, &fiq->pending); - wake_up_locked(&fiq->waitq); + wake_up(&fiq->waitq); kill_fasync(&fiq->fasync, SIGIO, POLL_IN); }

@@ -389,16 +389,16 @@ void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget, forget->forget_one.nodeid = nodeid; forget->forget_one.nlookup = nlookup;

- spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); if (fiq->connected) { fiq->forget_list_tail->next = forget; fiq->forget_list_tail = forget; - wake_up_locked(&fiq->waitq); + wake_up(&fiq->waitq); kill_fasync(&fiq->fasync, SIGIO, POLL_IN); } else { kfree(forget); } - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); }

static void flush_bg_queue(struct fuse_conn *fc) @@ -412,10 +412,10 @@ static void flush_bg_queue(struct fuse_conn *fc) req = list_first_entry(&fc->bg_queue, struct fuse_req, list); list_del(&req->list); fc->active_background++; - spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); req->in.h.unique = fuse_get_unique(fiq); queue_request(fiq, req); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); } }

@@ -439,9 +439,9 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req) * smp_mb() from queue_interrupt(). */ if (!list_empty(&req->intr_entry)) { - spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); list_del_init(&req->intr_entry); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); } WARN_ON(test_bit(FR_PENDING, &req->flags)); WARN_ON(test_bit(FR_SENT, &req->flags)); @@ -483,10 +483,10 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)

static int queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req) { - spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); /* Check for we've sent request to interrupt this req */ if (unlikely(!test_bit(FR_INTERRUPTED, &req->flags))) { - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); return -EINVAL; }

@@ -499,13 +499,13 @@ static int queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req) smp_mb(); if (test_bit(FR_FINISHED, &req->flags)) { list_del_init(&req->intr_entry); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); return 0; } - wake_up_locked(&fiq->waitq); + wake_up(&fiq->waitq); kill_fasync(&fiq->fasync, SIGIO, POLL_IN); } - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); return 0; }

@@ -535,16 +535,16 @@ static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req) if (!err) return;

- spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); /* Request is not yet in userspace, bail out */ if (test_bit(FR_PENDING, &req->flags)) { list_del(&req->list); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); __fuse_put_request(req); req->out.h.error = -EINTR; return; } - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); }

/* @@ -559,9 +559,9 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req) struct fuse_iqueue *fiq = &fc->iq;

BUG_ON(test_bit(FR_BACKGROUND, &req->flags)); - spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); if (!fiq->connected) { - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); req->out.h.error = -ENOTCONN; } else { req->in.h.unique = fuse_get_unique(fiq); @@ -569,7 +569,7 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req) /* acquire extra reference, since request is still needed after request_end() */ __fuse_get_request(req); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock);

request_wait_answer(fc, req); /* Pairs with smp_wmb() in request_end() */ @@ -700,12 +700,12 @@ static int fuse_request_send_notify_reply(struct fuse_conn *fc,

__clear_bit(FR_ISREPLY, &req->flags); req->in.h.unique = unique; - spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); if (fiq->connected) { queue_request(fiq, req); err = 0; } - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock);

return err; } @@ -1149,12 +1149,12 @@ static int request_pending(struct fuse_iqueue *fiq) * Unlike other requests this is assembled on demand, without a need * to allocate a separate fuse_req structure. * - * Called with fiq->waitq.lock held, releases it + * Called with fiq->lock held, releases it */ static int fuse_read_interrupt(struct fuse_iqueue *fiq, struct fuse_copy_state *cs, size_t nbytes, struct fuse_req *req) -__releases(fiq->waitq.lock) +__releases(fiq->lock) { struct fuse_in_header ih; struct fuse_interrupt_in arg; @@ -1169,7 +1169,7 @@ __releases(fiq->waitq.lock) ih.unique = (req->in.h.unique | FUSE_INT_REQ_BIT); arg.unique = req->in.h.unique;

- spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); if (nbytes < reqsize) return -EINVAL;

@@ -1206,7 +1206,7 @@ static struct fuse_forget_link *dequeue_forget(struct fuse_iqueue *fiq, static int fuse_read_single_forget(struct fuse_iqueue *fiq, struct fuse_copy_state *cs, size_t nbytes) -__releases(fiq->waitq.lock) +__releases(fiq->lock) { int err; struct fuse_forget_link *forget = dequeue_forget(fiq, 1, NULL); @@ -1220,7 +1220,7 @@ __releases(fiq->waitq.lock) .len = sizeof(ih) + sizeof(arg), };

- spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); kfree(forget); if (nbytes < ih.len) return -EINVAL; @@ -1238,7 +1238,7 @@ __releases(fiq->waitq.lock)

static int fuse_read_batch_forget(struct fuse_iqueue *fiq, struct fuse_copy_state *cs, size_t nbytes) -__releases(fiq->waitq.lock) +__releases(fiq->lock) { int err; unsigned max_forgets; @@ -1252,13 +1252,13 @@ __releases(fiq->waitq.lock) };

if (nbytes < ih.len) { - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); return -EINVAL; }

max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one); head = dequeue_forget(fiq, max_forgets, &count); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock);

arg.count = count; ih.len += count * sizeof(struct fuse_forget_one); @@ -1288,7 +1288,7 @@ __releases(fiq->waitq.lock) static int fuse_read_forget(struct fuse_conn *fc, struct fuse_iqueue *fiq, struct fuse_copy_state *cs, size_t nbytes) -__releases(fiq->waitq.lock) +__releases(fiq->lock) { if (fc->minor < 16 || fiq->forget_list_head.next->next == NULL) return fuse_read_single_forget(fiq, cs, nbytes); @@ -1336,16 +1336,19 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, return -EINVAL;

restart: - spin_lock(&fiq->waitq.lock); - err = -EAGAIN; - if ((file->f_flags & O_NONBLOCK) && fiq->connected && - !request_pending(fiq)) - goto err_unlock; + for (;;) { + spin_lock(&fiq->lock); + if (!fiq->connected || request_pending(fiq)) + break; + spin_unlock(&fiq->lock);

- err = wait_event_interruptible_exclusive_locked(fiq->waitq, + if (file->f_flags & O_NONBLOCK) + return -EAGAIN; + err = wait_event_interruptible_exclusive(fiq->waitq, !fiq->connected || request_pending(fiq)); - if (err) - goto err_unlock; + if (err) + return err; + }

if (!fiq->connected) { err = fc->aborted ? -ECONNABORTED : -ENODEV; @@ -1369,7 +1372,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, req = list_entry(fiq->pending.next, struct fuse_req, list); clear_bit(FR_PENDING, &req->flags); list_del_init(&req->list); - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock);

in = &req->in; reqsize = in->h.len; @@ -1427,7 +1430,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, return err;

err_unlock: - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock); return err; }

@@ -2139,12 +2142,12 @@ static __poll_t fuse_dev_poll(struct file *file, poll_table *wait) fiq = &fud->fc->iq; poll_wait(file, &fiq->waitq, wait);

- spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); if (!fiq->connected) mask = EPOLLERR; else if (request_pending(fiq)) mask |= EPOLLIN | EPOLLRDNORM; - spin_unlock(&fiq->waitq.lock); + spin_unlock(&fiq->lock);

return mask; } @@ -2239,15 +2242,15 @@ void fuse_abort_conn(struct fuse_conn *fc) flush_bg_queue(fc); spin_unlock(&fc->bg_lock);

- spin_lock(&fiq->waitq.lock); + spin_lock(&fiq->lock); fiq->connected = 0; list_for_each_entry(req, &fiq->pending, list) clear_bit(FR_PENDING, &req->flags); list_splice_tail_init(&fiq->pending, &to_end); while (forget_pending(fiq)) kfree(dequeue_forget(fiq, 1, NULL)); - wake_up_all_locked(&fiq->waitq); - spin_unlock(&fiq->waitq.lock); + wake_up_all(&fiq->waitq); + spin_unlock(&fiq->lock); kill_fasync(&fiq->fasync, SIGIO, POLL_IN); end_polls(fc); wake_up_all(&fc->blocked_waitq); diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index 24dbca777775..89bdc41e0d86 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -450,6 +450,9 @@ struct fuse_iqueue { /** Connection established */ unsigned connected;

+ /** Lock protecting accesses to members of this structure */ + spinlock_t lock; + /** Readers of the connection are waiting on this */ wait_queue_head_t waitq;

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index 2183967261a4..9ae9fdd5a014 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -589,6 +589,7 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root) static void fuse_iqueue_init(struct fuse_iqueue *fiq) { memset(fiq, 0, sizeof(struct fuse_iqueue)); + spin_lock_init(&fiq->lock); init_waitqueue_head(&fiq->waitq); INIT_LIST_HEAD(&fiq->pending); INIT_LIST_HEAD(&fiq->interrupts);