linux-kernel - Re: [RFC PATCH] initramfs: finish fput() before accessing any binary from initramfs

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Date:   Tue, 17 Jan 2017 14:53:08 +0200
From:   Tero Kristo <t-kristo@...com>
To:     Lokesh Vutla <lokeshvutla@...com>, <viro@...iv.linux.org.uk>
CC:     <linux-kernel@...r.kernel.org>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Sekhar Nori <nsekhar@...com>, Nishanth Menon <nm@...com>
Subject: Re: [RFC PATCH] initramfs: finish fput() before accessing any binary
 from initramfs

On 17/01/17 13:14, Lokesh Vutla wrote:
> commit 4a9d4b024a31 ("switch fput to task_work_add") implements a
> schedule_work() for completing fput(), but did not guarantee calling
> __fput() after unpacking initramfs. Because of this, there is a
> possibility that during boot a driver can see ETXTBSY when it tries
> to load a binary from initramfs as fput() is still pending on that
> binary. This patch makes sure that fput() is completed after unpacking
> initramfs.

Good find there.

>
> Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
> ---
>
> - Reproduced on TI K2HK EVM. K2HK Queue Manager subsystem driver[1] tries
> to load a firmware from initramfs during boot. Sometimes loading of this
> firmware fails with error ETXTBSY. Digging a bit more observed that
> deny_write_access() is returning ETXTBSY as inode->i_writecount is > 0
> for that file. This is because Unpacking initramfs does a
> get_write_access(from open) but hasn't done put_write_access(from fput)
> as it hasn't been scheduled yet.
>
> [1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/ti/knav_qmss_queue.c
>
>  init/initramfs.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/init/initramfs.c b/init/initramfs.c
> index b32ad7d97ac9..c42c69b48a4b 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -18,6 +18,7 @@
>  #include <linux/dirent.h>
>  #include <linux/syscalls.h>
>  #include <linux/utime.h>
> +#include <linux/file.h>
>
>  static ssize_t __init xwrite(int fd, const char *p, size_t count)
>  {
> @@ -652,6 +653,7 @@ static int __init populate_rootfs(void)
>  		 * us a chance to load before device_initcalls.
>  		 */
>  		load_default_modules();
> +		flush_delayed_fput();

Shouldn't the flush be called before the load_default_modules() though?

-Tero