From: Luis Chamberlain <mcgrof@kernel.org>
To: Lukas Middendorf <kernel@tuxforce.de>,
Greg KH <gregkh@linuxfoundation.org>,
dsterba@suse.cz
Cc: linux-btrfs@vger.kernel.org, Antti Palosaari <crope@iki.fi>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
linux-media@vger.kernel.org
Subject: Re: Is request_firmware() really safe to call in resume callback when /usr/lib/firmware is on btrfs?
Date: Sat, 3 Apr 2021 21:04:44 +0000 [thread overview]
Message-ID: <20210403210444.GU13911@42.do-not-panic.com> (raw)
In-Reply-To: <20210403202538.GW4332@42.do-not-panic.com>
On Sat, Apr 03, 2021 at 08:25:38PM +0000, Luis Chamberlain wrote:
> So creating say 1000 random files in /lib/firmware on a freshly created
> btrfs partition helps reproduce:
>
> mkfs.btrfs /dev/whatever
> mount /dev/wahtever /lib/firmware
> # Put it on /etc/fstab too
>
> Generate 1000 random files on it:
>
> ```
> for n in {1..1000}; do
> dd if=/dev/urandom of=/lib/firmware/file$( printf %03d "$n" ).bin bs=1 count=$((RANDOM + 1024 ))
> done
> ```
>
> Then reboot, upon reboot do:
>
> modprobe test_firmware
> echo 1 > /sys/devices/virtual/misc/test_firmware/config_enable_resume_test
> systemctl suspend
OK this fixes it but this just shows that likely the thaw'ing allows
a race to take place which we didn't expect. I'll do some more digging
for a proper fix.
diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index 90d255fbdd9b..b9c37eefab35 100644
--- a/fs/kernel_read_file.c
+++ b/fs/kernel_read_file.c
@@ -4,6 +4,7 @@
#include <linux/kernel_read_file.h>
#include <linux/security.h>
#include <linux/vmalloc.h>
+#include <linux/umh.h>
/**
* kernel_read_file() - read file contents into a kernel buffer
@@ -156,17 +157,25 @@ int kernel_read_file_from_path_initns(const char *path, loff_t offset,
if (!path || !*path)
return -EINVAL;
+ ret = usermodehelper_read_trylock();
+ if (WARN_ON(ret)) {
+ pr_warn_once("Trying to do direct read when not available");
+ return ret;
+ }
task_lock(&init_task);
get_fs_root(init_task.fs, &root);
task_unlock(&init_task);
file = file_open_root(root.dentry, root.mnt, path, O_RDONLY, 0);
path_put(&root);
- if (IS_ERR(file))
+ if (IS_ERR(file)) {
+ usermodehelper_read_unlock();
return PTR_ERR(file);
+ }
ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
fput(file);
+ usermodehelper_read_unlock();
return ret;
}
EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
next prev parent reply other threads:[~2021-04-03 21:04 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-09 18:51 Is request_firmware() really safe to call in resume callback when /usr/lib/firmware is on btrfs? Lukas Middendorf
2020-08-13 16:37 ` Luis Chamberlain
2020-08-13 21:53 ` Lukas Middendorf
2020-08-13 22:13 ` Luis Chamberlain
2020-08-14 11:38 ` Lukas Middendorf
2020-08-14 16:37 ` Luis Chamberlain
2020-08-14 21:59 ` Lukas Middendorf
2020-08-17 15:20 ` Luis Chamberlain
2020-08-17 22:04 ` Lukas Middendorf
2020-08-18 14:37 ` Luis Chamberlain
2021-04-01 14:59 ` Lukas Middendorf
2021-04-02 18:02 ` Luis Chamberlain
2021-04-02 22:19 ` Luis Chamberlain
2021-04-02 22:58 ` Luis Chamberlain
2021-04-03 10:24 ` Lukas Middendorf
2021-04-03 16:07 ` Lukas Middendorf
2021-04-03 20:25 ` Luis Chamberlain
2021-04-03 21:04 ` Luis Chamberlain [this message]
2021-04-05 9:52 ` Lukas Middendorf
2021-04-04 0:50 ` Lukas Middendorf
2021-04-08 18:02 ` Luis Chamberlain
2021-04-16 23:17 ` Luis Chamberlain
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