linux.git/sound/core/info.c, branch v5.10.258

ALSA: info: Fix potential deadlock at disconnection

2023-11-28T16:54:59+00:00

commit c7a60651953359f98dbf24b43e1bf561e1573ed4 upstream.

As reported recently, ALSA core info helper may cause a deadlock at
the forced device disconnection during the procfs operation.

The proc_remove() (that is called from the snd_card_disconnect()
helper) has a synchronization of the pending procfs accesses via
wait_for_completion().  Meanwhile, ALSA procfs helper takes the global
mutex_lock(&info_mutex) at both the proc_open callback and
snd_card_info_disconnect() helper.  Since the proc_open can't finish
due to the mutex lock, wait_for_completion() never returns, either,
hence it deadlocks.

	TASK#1				TASK#2
	proc_reg_open()
	  takes use_pde()
	snd_info_text_entry_open()
					snd_card_disconnect()
					snd_info_card_disconnect()
					  takes mutex_lock(&info_mutex)
					proc_remove()
					wait_for_completion(unused_pde)
					  ... waiting task#1 closes
	mutex_lock(&info_mutex)
		=> DEADLOCK

This patch is a workaround for avoiding the deadlock scenario above.

The basic strategy is to move proc_remove() call outside the mutex
lock.  proc_remove() can work gracefully without extra locking, and it
can delete the tree recursively alone.  So, we call proc_remove() at
snd_info_card_disconnection() at first, then delete the rest resources
recursively within the info_mutex lock.

After the change, the function snd_info_disconnect() doesn't do
disconnection by itself any longer, but it merely clears the procfs
pointer.  So rename the function to snd_info_clear_entries() for
avoiding confusion.

The similar change is applied to snd_info_free_entry(), too.  Since
the proc_remove() is called only conditionally with the non-NULL
entry->p, it's skipped after the snd_info_clear_entries() call.

Reported-by: Shinhyung Kang 
Closes: https://lore.kernel.org/r/664457955.21699345385931.JavaMail.epsvc@epcpadp4
Reviewed-by: Jaroslav Kysela 
Cc: 
Link: https://lore.kernel.org/r/20231109141954.4283-1-tiwai@suse.de
Signed-off-by: Takashi Iwai 
Signed-off-by: Greg Kroah-Hartman

ALSA: info: Fix llseek return value when using callback

2022-08-25T09:37:49+00:00

commit 9be080edcca330be4af06b19916c35227891e8bc upstream.

When using callback there was a flow of

	ret = -EINVAL
	if (callback) {
		offset = callback();
		goto out;
	}
	...
	offset = some other value in case of no callback;
	ret = offset;
out:
	return ret;

which causes the snd_info_entry_llseek() to return -EINVAL when there is
callback handler. Fix this by setting "ret" directly to callback return
value before jumping to "out".

Fixes: 73029e0ff18d ("ALSA: info - Implement common llseek for binary mode")
Signed-off-by: Amadeusz Sławiński 
Cc: 
Link: https://lore.kernel.org/r/20220817124924.3974577-1-amadeuszx.slawinski@linux.intel.com
Signed-off-by: Takashi Iwai 
Signed-off-by: Greg Kroah-Hartman

ALSA: info: Drop WARN_ON() from buffer NULL sanity check

2020-07-17T08:59:38+00:00

snd_info_get_line() has a sanity check of NULL buffer -- both buffer
itself being NULL and buffer->buffer being NULL.  Basically both
checks are valid and necessary, but the problem is that it's with
snd_BUG_ON() macro that triggers WARN_ON().  The latter condition
(NULL buffer->buffer) can be met arbitrarily by user since the buffer
is allocated at the first write, so it means that user can trigger
WARN_ON() at will.

This patch addresses it by simply moving buffer->buffer NULL check out
of snd_BUG_ON() so that spurious WARNING is no longer triggered.

Reported-by: syzbot+e42d0746c3c3699b6061@syzkaller.appspotmail.com
Cc: 
Link: https://lore.kernel.org/r/20200717084023.5928-1-tiwai@suse.de
Signed-off-by: Takashi Iwai

ALSA: info: remove redundant assignment to variable c

2020-02-10T07:30:02+00:00

Variable c is being assigned with the value -1 that is never read,
it is assigned a new value in a following while-loop. The assignment
is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King 
Link: https://lore.kernel.org/r/20200208224206.38540-1-colin.king@canonical.com
Signed-off-by: Takashi Iwai

proc: convert everything to "struct proc_ops"

2020-02-04T03:05:26+00:00

The most notable change is DEFINE_SHOW_ATTRIBUTE macro split in
seq_file.h.

Conversion rule is:

	llseek		=> proc_lseek
	unlocked_ioctl	=> proc_ioctl

	xxx		=> proc_xxx

	delete ".owner = THIS_MODULE" line

[akpm@linux-foundation.org: fix drivers/isdn/capi/kcapi_proc.c]
[sfr@canb.auug.org.au: fix kernel/sched/psi.c]
  Link: http://lkml.kernel.org/r/20200122180545.36222f50@canb.auug.org.au
Link: http://lkml.kernel.org/r/20191225172546.GB13378@avx2
Signed-off-by: Alexey Dobriyan 
Signed-off-by: Stephen Rothwell 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ALSA: info: More constifications

2020-01-05T15:14:57+00:00

Apply const prefix to the string array and its callers.

Just for minor optimization and no functional changes.

Link: https://lore.kernel.org/r/20200105144823.29547-39-tiwai@suse.de
Signed-off-by: Takashi Iwai

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156

2019-05-30T18:26:35+00:00

Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license as published by
  the free software foundation either version 2 of the license or at
  your option any later version this program is distributed in the
  hope that it will be useful but without any warranty without even
  the implied warranty of merchantability or fitness for a particular
  purpose see the gnu general public license for more details you
  should have received a copy of the gnu general public license along
  with this program if not write to the free software foundation inc
  59 temple place suite 330 boston ma 02111 1307 usa

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 1334 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Allison Randal 
Reviewed-by: Richard Fontana 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070033.113240726@linutronix.de
Signed-off-by: Greg Kroah-Hartman

ALSA: info: Fix racy addition/deletion of nodes

2019-04-16T13:49:48+00:00

The ALSA proc helper manages the child nodes in a linked list, but its
addition and deletion is done without any lock.  This leads to a
corruption if they are operated concurrently.  Usually this isn't a
problem because the proc entries are added sequentially in the driver
probe procedure itself.  But the card registrations are done often
asynchronously, and the crash could be actually reproduced with
syzkaller.

This patch papers over it by protecting the link addition and deletion
with the parent's mutex.  There is "access" mutex that is used for the
file access, and this can be reused for this purpose as well.

Reported-by: syzbot+48df349490c36f9f54ab@syzkaller.appspotmail.com
Cc: 
Signed-off-by: Takashi Iwai

ALSA: info: Move card id proc creation into info.c

2019-02-06T17:11:58+00:00

The creation of card's id proc file can be moved gracefully into
info.c.  Also, the assignment of card->proc_id is superfluous and can
be dropped.  So let's do it.

Basically this is no functional change but code refactoring, but one
potential behavior change is that now it returns properly the error
code from snd_info_card_register(), which is a good thing (tm).

Reviewed-by: Jaroslav Kysela 
Signed-off-by: Takashi Iwai

ALSA: info: Minor optimization

2019-02-06T17:11:58+00:00

Just a minor code optimization to reduce the source code size
slightly.  No functional changes.

Reviewed-by: Jaroslav Kysela 
Signed-off-by: Takashi Iwai