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Boqun Feng 642c2d74c3 fcntl: Fix potential deadlock in send_sig{io, urg}() 
commit 8d1ddb5e79 upstream.

Syzbot reports a potential deadlock found by the newly added recursive
read deadlock detection in lockdep:

[...] ========================================================
[...] WARNING: possible irq lock inversion dependency detected
[...] 5.9.0-rc2-syzkaller #0 Not tainted
[...] --------------------------------------------------------
[...] syz-executor.1/10214 just changed the state of lock:
[...] ffff88811f506338 (&f->f_owner.lock){.+..}-{2:2}, at: send_sigurg+0x1d/0x200
[...] but this lock was taken by another, HARDIRQ-safe lock in the past:
[...]  (&dev->event_lock){-...}-{2:2}
[...]
[...]
[...] and interrupts could create inverse lock ordering between them.
[...]
[...]
[...] other info that might help us debug this:
[...] Chain exists of:
[...]   &dev->event_lock --> &new->fa_lock --> &f->f_owner.lock
[...]
[...]  Possible interrupt unsafe locking scenario:
[...]
[...]        CPU0                    CPU1
[...]        ----                    ----
[...]   lock(&f->f_owner.lock);
[...]                                local_irq_disable();
[...]                                lock(&dev->event_lock);
[...]                                lock(&new->fa_lock);
[...]   <Interrupt>
[...]     lock(&dev->event_lock);
[...]
[...]  *** DEADLOCK ***

The corresponding deadlock case is as followed:

	CPU 0		CPU 1		CPU 2
	read_lock(&fown->lock);
			spin_lock_irqsave(&dev->event_lock, ...)
					write_lock_irq(&filp->f_owner.lock); // wait for the lock
			read_lock(&fown-lock); // have to wait until the writer release
					       // due to the fairness
	<interrupted>
	spin_lock_irqsave(&dev->event_lock); // wait for the lock

The lock dependency on CPU 1 happens if there exists a call sequence:

	input_inject_event():
	  spin_lock_irqsave(&dev->event_lock,...);
	  input_handle_event():
	    input_pass_values():
	      input_to_handler():
	        handler->event(): // evdev_event()
	          evdev_pass_values():
	            spin_lock(&client->buffer_lock);
	            __pass_event():
	              kill_fasync():
	                kill_fasync_rcu():
	                  read_lock(&fa->fa_lock);
	                  send_sigio():
	                    read_lock(&fown->lock);

To fix this, make the reader in send_sigurg() and send_sigio() use
read_lock_irqsave() and read_lock_irqrestore().

Reported-by: syzbot+22e87cdf94021b984aa6@syzkaller.appspotmail.com
Reported-by: syzbot+c5e32344981ad9f33750@syzkaller.appspotmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2021-01-06 14:48:39 +01:00
Documentation x86/CPU/AMD: Save AMD NodeId as cpu_die_id 2020-12-30 11:51:47 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch powerpc/bitops: Fix possible undefined behaviour with fls() and fls64() 2021-01-06 14:48:36 +01:00
block scsi: block: Fix a race in the runtime power management code 2021-01-06 14:48:37 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: ecdh - avoid unaligned accesses in ecdh_set_secret() 2020-12-30 11:51:35 +01:00
drivers media: gp8psk: initialize stats at power control logic 2021-01-06 14:48:38 +01:00
fs fcntl: Fix potential deadlock in send_sig{io, urg}() 2021-01-06 14:48:39 +01:00
include of: fix linker-section match-table corruption 2021-01-06 14:48:37 +01:00
init initramfs: fix clang build failure 2020-12-30 11:51:30 +01:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel cgroup: Fix memory leak when parsing multiple source parameters 2021-01-06 14:48:37 +01:00
lib lib/syscall: fix syscall registers retrieval on 32-bit platforms 2020-12-11 13:23:32 +01:00
mm mm: don't wake kswapd prematurely when watermark boosting is disabled 2020-12-30 11:51:27 +01:00
net net/sched: sch_taprio: reset child qdiscs before freeing them 2021-01-06 14:48:35 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts kconfig: fix return value of do_error_if() 2020-12-30 11:51:29 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:51:39 +01:00
sound ALSA: rawmidi: Access runtime->avail always in spinlock 2021-01-06 14:48:38 +01:00
tools tools headers UAPI: Sync linux/const.h with the kernel headers 2021-01-06 14:48:37 +01:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm64: vgic-v3: Drop the reporting of GICR_TYPER.Last for userspace 2020-12-02 08:49:46 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-08-26 10:40:46 +02:00
Makefile Linux 5.4.86 2020-12-30 11:51:48 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.