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

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Date:   Wed, 18 Jan 2017 11:21:11 +0530
From:   Lokesh Vutla <lokeshvutla@...com>
To:     Tero Kristo <t-kristo@...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 Tuesday 17 January 2017 06:23 PM, Tero Kristo wrote:
> 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?

Good point. Will wait for sometime for more comments and then repost it.

Thanks and regards,
Lokesh