kernfs: cache atomic_write_len in kernfs_open_file
While implementing atomic_write_len, 4d3773c4bb41 ("kernfs: implement
kernfs_ops->atomic_write_len") moved data copy from userland inside
kernfs_get_active() and kernfs_open_file->mutex so that
kernfs_ops->atomic_write_len can be accessed before copying buffer
from userland; unfortunately, this could lead to locking order
inversion involving mmap_sem if copy_from_user() takes a page fault.
======================================================
[ INFO: possible circular locking dependency detected ]
3.14.0-rc4-next-20140228-sasha-00011-g4077c67-dirty #26 Tainted: G W
-------------------------------------------------------
trinity-c236/10658 is trying to acquire lock:
(&of->mutex#2){+.+.+.}, at: [<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
but task is already holding lock:
(&mm->mmap_sem){++++++}, at: [<mm/util.c:397>] vm_mmap_pgoff+0x6e/0xe0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&mm->mmap_sem){++++++}:
[<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
[<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
[<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
[<mm/memory.c:4188>] might_fault+0x7e/0xb0
[<arch/x86/include/asm/uaccess.h:713 fs/kernfs/file.c:291>] kernfs_fop_write+0xd8/0x190
[<fs/read_write.c:473>] vfs_write+0xe3/0x1d0
[<fs/read_write.c:523 fs/read_write.c:515>] SyS_write+0x5d/0xa0
[<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
-> #0 (&of->mutex#2){+.+.+.}:
[<kernel/locking/lockdep.c:1840>] check_prev_add+0x13f/0x560
[<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
[<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
[<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
[<kernel/locking/mutex.c:470 kernel/locking/mutex.c:571>] mutex_lock_nested+0x6a/0x510
[<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
[<mm/mmap.c:1573>] mmap_region+0x310/0x5c0
[<mm/mmap.c:1365>] do_mmap_pgoff+0x385/0x430
[<mm/util.c:399>] vm_mmap_pgoff+0x8f/0xe0
[<mm/mmap.c:1416 mm/mmap.c:1374>] SyS_mmap_pgoff+0x1b0/0x210
[<arch/x86/kernel/sys_x86_64.c:72>] SyS_mmap+0x1d/0x20
[<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&mm->mmap_sem);
lock(&of->mutex#2);
lock(&mm->mmap_sem);
lock(&of->mutex#2);
*** DEADLOCK ***
1 lock held by trinity-c236/10658:
#0: (&mm->mmap_sem){++++++}, at: [<mm/util.c:397>] vm_mmap_pgoff+0x6e/0xe0
stack backtrace:
CPU: 2 PID: 10658 Comm: trinity-c236 Tainted: G W 3.14.0-rc4-next-20140228-sasha-00011-g4077c67-dirty #26
0000000000000000 ffff88011911fa48 ffffffff8438e945 0000000000000000
0000000000000000 ffff88011911fa98 ffffffff811a0109 ffff88011911fab8
ffff88011911fab8 ffff88011911fa98 ffff880119128cc0 ffff880119128cf8
Call Trace:
[<lib/dump_stack.c:52>] dump_stack+0x52/0x7f
[<kernel/locking/lockdep.c:1213>] print_circular_bug+0x129/0x160
[<kernel/locking/lockdep.c:1840>] check_prev_add+0x13f/0x560
[<include/linux/spinlock.h:343 mm/slub.c:1933>] ? deactivate_slab+0x511/0x550
[<kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131>] validate_chain+0x6c5/0x7b0
[<kernel/locking/lockdep.c:3182>] __lock_acquire+0x4cd/0x5a0
[<mm/mmap.c:1552>] ? mmap_region+0x24a/0x5c0
[<arch/x86/include/asm/current.h:14 kernel/locking/lockdep.c:3602>] lock_acquire+0x182/0x1d0
[<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
[<kernel/locking/mutex.c:470 kernel/locking/mutex.c:571>] mutex_lock_nested+0x6a/0x510
[<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
[<kernel/sched/core.c:2477>] ? get_parent_ip+0x11/0x50
[<fs/kernfs/file.c:487>] ? kernfs_fop_mmap+0x54/0x120
[<fs/kernfs/file.c:487>] kernfs_fop_mmap+0x54/0x120
[<mm/mmap.c:1573>] mmap_region+0x310/0x5c0
[<mm/mmap.c:1365>] do_mmap_pgoff+0x385/0x430
[<mm/util.c:397>] ? vm_mmap_pgoff+0x6e/0xe0
[<mm/util.c:399>] vm_mmap_pgoff+0x8f/0xe0
[<kernel/rcu/update.c:97>] ? __rcu_read_unlock+0x44/0xb0
[<fs/file.c:641>] ? dup_fd+0x3c0/0x3c0
[<mm/mmap.c:1416 mm/mmap.c:1374>] SyS_mmap_pgoff+0x1b0/0x210
[<arch/x86/kernel/sys_x86_64.c:72>] SyS_mmap+0x1d/0x20
[<arch/x86/kernel/entry_64.S:749>] tracesys+0xdd/0xe2
Fix it by caching atomic_write_len in kernfs_open_file during open so
that it can be determined without accessing kernfs_ops in
kernfs_fop_write(). This restores the structure of kernfs_fop_write()
before 4d3773c4bb41 with updated @len determination logic.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
References: http://lkml.kernel.org/g/53113485.2090407@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index ddcb471..8034706 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -253,8 +253,26 @@
{
struct kernfs_open_file *of = kernfs_of(file);
const struct kernfs_ops *ops;
- char *buf = NULL;
- ssize_t len;
+ size_t len;
+ char *buf;
+
+ if (of->atomic_write_len) {
+ len = count;
+ if (len > of->atomic_write_len)
+ return -E2BIG;
+ } else {
+ len = min_t(size_t, count, PAGE_SIZE);
+ }
+
+ buf = kmalloc(len + 1, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ if (copy_from_user(buf, user_buf, len)) {
+ len = -EFAULT;
+ goto out_free;
+ }
+ buf[len] = '\0'; /* guarantee string termination */
/*
* @of->mutex nests outside active ref and is just to ensure that
@@ -263,45 +281,22 @@
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
mutex_unlock(&of->mutex);
- return -ENODEV;
+ len = -ENODEV;
+ goto out_free;
}
ops = kernfs_ops(of->kn);
- if (!ops->write) {
+ if (ops->write)
+ len = ops->write(of, buf, len, *ppos);
+ else
len = -EINVAL;
- goto out_unlock;
- }
- if (ops->atomic_write_len) {
- len = count;
- if (len > ops->atomic_write_len) {
- len = -E2BIG;
- goto out_unlock;
- }
- } else {
- len = min_t(size_t, count, PAGE_SIZE);
- }
-
- buf = kmalloc(len + 1, GFP_KERNEL);
- if (!buf) {
- len = -ENOMEM;
- goto out_unlock;
- }
-
- if (copy_from_user(buf, user_buf, len)) {
- len = -EFAULT;
- goto out_unlock;
- }
- buf[len] = '\0'; /* guarantee string termination */
-
- len = ops->write(of, buf, len, *ppos);
-out_unlock:
kernfs_put_active(of->kn);
mutex_unlock(&of->mutex);
if (len > 0)
*ppos += len;
-
+out_free:
kfree(buf);
return len;
}
@@ -666,6 +661,12 @@
of->file = file;
/*
+ * Write path needs to atomic_write_len outside active reference.
+ * Cache it in open_file. See kernfs_fop_write() for details.
+ */
+ of->atomic_write_len = ops->atomic_write_len;
+
+ /*
* Always instantiate seq_file even if read access doesn't use
* seq_file or is not requested. This unifies private data access
* and readable regular files are the vast majority anyway.