[EXTERNAL] Re: [PATCH 0/4] fs: ubifs: Fix crash and add safeguards
Heiko Schocher
hs at denx.de
Mon Aug 5 07:28:19 CEST 2024
Hello Ravi,
On 01.08.24 21:39, Ravi Minnikanti wrote:
> Hi Heiko, Alexander,
>
> On 7/31/24 23:54, Heiko Schocher wrote:
>> Hello Alexander, On 01. 08. 24 08: 50, Alexander Dahl wrote: > Hei, > > Am Thu,
>> Jul 04, 2024 at 10: 18: 55AM +0200 schrieb Alexander Dahl: >> Hello Heiko, >> >>
>> Am Thu, Jul 04, 2024 at 06: 28: 31AM +0200 schrieb Heiko Schocher:
>>
>>
>> Hello Alexander,
>>
>> On 01.08.24 08:50, Alexander Dahl wrote:
>>> Hei,
>>>
>>> Am Thu, Jul 04, 2024 at 10:18:55AM +0200 schrieb Alexander Dahl:
>>>> Hello Heiko,
>>>>
>>>> Am Thu, Jul 04, 2024 at 06:28:31AM +0200 schrieb Heiko Schocher:
>>>>> Hello Alexander,
>>>>>
>>>>> On 03.07.24 12:12, Alexander Dahl wrote:
>>>>>> Hei hei,
>>>>>>
>>>>>> filesystem handling is different in U-Boot and beyond that UBI/UBIFS is
>>>>>> different from other filesystems in U-Boot. There's UBI and UBIFS code
>>>>>> ported from Linux (quite old already now, maybe someone wants to update
>>>>>> that?), and there's "glue code" or "wrapper code" to interface with
>>>>>> U-Boot scripts, commands, and filesystem handling. The fixes and
>>>>>> improvements in this patch series are for this U-Boot specific glue
>>>>>> code.
>>>>>
>>>>> Yes, the linux base is very old ... patches are welcome!
>>>>
>>>> The last sync was back in 2015 from linux v4.2, there were 800+
>>>> changes to ubi/ubifs in Linux since then. :-/
>>>>
>>>>> And for me it is not that easy, as I do not have a hardware with
>>>>> current mainline U-Boot running on it... I want to update a hardware
>>>>> I have to current mainline, but I had no time yet for it...
>>>>
>>>> Besides the custom hardware here, I used Microchip SAM9X60-Curiosity
>>>> lately, which is coming with a raw NAND flash and can boot from it.
>>>>
>>>>>
>>>>>> I'm no filesystem expert, but after days of debugging I'm quite sure the
>>>>>> bug is in U-Boot since UBIFS support was added in 2009, and it was
>>>>>> repeated in 2015 when generic filesystem support for UBIFS was added.
>>>>>> So please review carefully!
>>>>>
>>>>> Which bug?
>>>>
>>>> The memory leak and double free fixed with patch 1 of the series.
>>>>
>>>>>
>>>>>> The crashes were not easily reproducible, only with boards using the old
>>>>>> distroboot _and_ a boot script inspired by (but not equal to) the one
>>>>>> proposed by RAUC [1], which basically boils down to:
>>>>>>
>>>>>> ubifsmount ubi0:boot (from distroboot)
>>>>>> test -e (from distroboot)
>>>>>> ubifsmount ubi0:rootfs1 (this time from the boot script,
>>>>>> triggering a ubifs_umount)
>>>>>
>>>>> So, you have a special sequence you execute to trigger the bug, good!
>>>>>
>>>>> In special 2 ubifsmount in a row... may not often needed for booting!
>>>>> (I ask me, why that is needed? Boottime is not good than...)
>>>>
>>>> Using distroboot with a script here. The script is in a separate UBI
>>>> volume ubi0:boot, kernel is loaded from ubi0:rootfs1 or ubi0:rootfs2
>>>> however. So there is 'ubifsmount ubi0:boot' from distroboot and in the
>>>> script found, loaded, and run there is 'ubifsmount ubi0:rootfs1' (or
>>>> rootfs2) later. ubifsmount calls ubifsumount internally if some
>>>> volume is mounted already.
>>>>
>>>>>
>>>>> BTW: Is this really a good bootcmd in [1] as on *every* boot your
>>>>> Environment is saved? This is not good for lifetime of your
>>>>> storage device ... why not using bootcounter?
>>>>
>>>> Well, I was not aware of bootcounter, but I had a look and the actual
>>>> counter must be stored somewhere. Possible are:
>>>>
>>>> - pmic → has no storage possibility on my board
>>>> - rtc → soc internal only, volatile in the end (if battery is empty)
>>>> - i2c eeprom → missing
>>>> - spi flash → missing
>>>> - filesystem → ends up on the flash
>>>> - nvmem → no other nvmems present
>>>> - syscon or some cpu register or sram → volatile
>>>>
>>>> So none of these are possible in my case, I only have a raw NAND as
>>>> storage and thus I have to use U-Boot env, which is stored in UBI here
>>>> btw to not stress the flash too much.
>>>>
>>>> I could investigate if it would be possible to let RAUC use the
>>>> U-Boot bootcounter infrastructure, but currently RAUC depends on
>>>> U-Boot environment variables for tracking boot attempts.
>>>>
>>>> btw: documentation of bootcount is sparse, I only found the very short
>>>> 'doc/README.bootcount' and it's not even migrated to recent U-Boot
>>>> sphinx based docs. ;-)
>>>>
>>>> But from what I understood the concept is the same, U-Boot counts
>>>> something and Linux userspace has to reset it. The counter must be
>>>> stored somewhere, for example in U-Boot env if no other storage is
>>>> possible.
>>>>
>>>>>
>>>>>> Crashes can be triggered more easily, if patch order is changed and
>>>>>> patch 2 (resetting pointers to NULL after free) comes first, or if patch
>>>>>> 2 is applied on its own only.
>>>>>
>>>>> Hmm...
>>>>>
>>>>>> The fix is in the first patch, and on my boards I see no crashes
>>>>>> anymore. I also tested all kinds of combinations of calling `ubi part`,
>>>>>> `ubi detach`, `ubifsmount`, `ubifsumount`, `ubifsls`, `ubifsload`, `ls`,
>>>>>> `load`, `size`, and `test -e` and got no crashes anymore after the fix.
>>>>>
>>>>> That sounds good! Hmm.. test -e has nothing to do with ubi/ubifs I think.
>>>>
>>>> Oh it has, 'test -e' calls file_exists() which calls fs_exists() which
>>>> ends up calling ubifs_exists() which is one of the functions causing
>>>> an immediate memory leak, see patch 1.
>>>>
>>>>> On what hardware do you test? Is it in mainline?
>>>>
>>>> Tested on custom hardware, but I'm confident it should be reproducible
>>>> on any board using ubifs, especially after applying patch 2 resetting
>>>> pointers of freed memory to NULL. This should trigger the bug with
>>>> the simple sequence already described:
>>>>
>>>> > ubifsmount ubi0:anyvolume
>>>> > ls ubi ubi0:anyvolume / # (or load, or test -e, or size)
>>>> > ubifsumount
>>>>
>>>> ubifsumount will call ubifs_umount() which calls
>>>> ubi_close_volume(c->ubi), that pointer is either invalid leading to a
>>>> double free inside of ubi_close_volume() and it will crash only in
>>>> certain conditions or the pointer is NULL after applying patch 2 of
>>>> the series, then ubi_close_volume() crashes right away with a NULL
>>>> pointer exception.
>>>>
>>>> Note: without patch 2 it very much depends on the sequence of
>>>> commands, but after the first ubi_close_volume() triggered by
>>>> ls/load/size/exists the pointer in ubifs_sb is invalid, but accessed later
>>>> by the second ubi_close_volume() triggered by ubifs_umount(). If you
>>>> do something in between those using the freed memory by something else
>>>> again, the second ubi_close_volume() access might get corrupted data
>>>> or access things outside of RAM. Patch 2 redirects this on a clean
>>>> NULL pointer exception you can easily trigger.
>>>>
>>>> In my case I got a pointer variable actually containing a string
>>>> "ng.." aka 0x2e2e676e which looked suspiciously similar to a valid
>>>> pointer on the platform somewhere in RAM between 0x20000000 and
>>>> 0x28000000 so it took me two days to realize it's not a pointer. ;-)
>>>>
>>>>>
>>>>>> The three additional patches (2 to 4) are more or less safeguards and
>>>>>> improvements for the future, and come from me trying and my debugging
>>>>>> code done on the way, more or less optional, but I think nice to have.
>>>>>
>>>>> I will look at them .. but give me some time, as I am in holidays the
>>>>> next 2 weeks ... Hmm.. and it would be good to get some Tested-by
>>>>> from people with hardware...
>>>>
>>>> Take your time, no need to work in holidays. Would appreciate a
>>>> Tested-by by anyone else though, maybe some of the raw NAND folks?
>>>
>>> Well, apparently nobody had a look in the month of July, I add the raw
>>> NAND maintainers in Cc, maybe I should have done in the first place.
>>>
>>> Would be happy if someone could have a look at the fix, maybe read the
>>> patches first before the discussion? ;-)
>>
>> I asked Ravi and Alexey (added to cc) if they have time to look it they
>> can reproduce the issue and test your patches...
>>
>> bye,
>> Heiko
>
> I tried to reproduce with CONFIG_SYS_MALLOC_LEN reduced to 1MB and
> calling ubifsls in a loop, logic below:
>
> ubi part ubi0:rootfs
> ubifsmount ubi0:rootfs
> setenv i 1
> while test $i -le 200; do
> ubifsls a/b/test.bin
> setexpr i $i + 1
> sleep 1
> echo "Loop count: $i"
> done
Thanks for testing! But it is not exactly the same sequence Alexander
described ... but you also trigger a bug.
> It crashes with or without patch. With patch it takes 4,5 loops more to crash.
>
> Log:
> UBIFS error (ubi0:0 pid 0): ubifs_iget: failed to read inode 85, error -12
> "Synchronous Abort" handler, esr 0x96000004
-12 = -ENOMEM
So it seems, we have a memleak...
Yes, ubi/ubifs linux base is very old, but I tend to think that problem is
in U-Boot adaption layer...
bye,
Heiko
>
>
> Thanks,
> Ravi
>>>
>>> Greets
>>> Alex
>>>
>>>>
>>>> Greets
>>>> Alex
>>>>
>>>>>
>>>>> bye,
>>>>> Heiko
>>>>>>
>>>>>> Greets
>>>>>> Alex
>>>>>>
>>>>>> [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_rauc_rauc_blob_master_contrib_uboot.sh&d=DwIDaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=3apjoJolwzwH82pd_c1HzSLzzrwfu9x1lSm802edgOg&m=lpy642UhqtTXHV0dd0xnOtQxkQSO5RC6FwcUbzt-FsNwd3QSXZsulfqC6dP9qV7G&s=wbnw_T9_r6taMKIFqJ2-wtj9Zv02OD7mbIy-ZZFRjRE&e= <https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_rauc_rauc_blob_master_contrib_uboot.sh&d=DwIDaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=3apjoJolwzwH82pd_c1HzSLzzrwfu9x1lSm802edgOg&m=lpy642UhqtTXHV0dd0xnOtQxkQSO5RC6FwcUbzt-FsNwd3QSXZsulfqC6dP9qV7G&s=wbnw_T9_r6taMKIFqJ2-wtj9Zv02OD7mbIy-ZZFRjRE&e=>
>>>>>>
>>>>>> Alexander Dahl (4):
>>>>>> fs: ubifs: Fix memleak and double free in u-boot wrapper functions
>>>>>> fs: ubifs: Set pointers to NULL after free
>>>>>> fs: ubifs: Make k(z)alloc/kfree symmetric
>>>>>> fs: ubifs: Add volume mounted check
>>>>>>
>>>>>> fs/ubifs/super.c | 8 ++++++--
>>>>>> fs/ubifs/ubifs.c | 31 +++++++++++++++++++------------
>>>>>> 2 files changed, 25 insertions(+), 14 deletions(-)
>>>>>>
>>>>>>
>>>>>> base-commit: 65fbdab27224ee3943a89496b21862db83c34da2
>>>>>>
>>>>>
>>>>> --
>>>>> DENX Software Engineering GmbH, Managing Director: Erika Unter
>>>>> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
>>>>> Phone: +49-8142-66989-52 Fax: +49-8142-66989-80 Email: hs at denx.de
>>
>> --
>> DENX Software Engineering GmbH, Managing Director: Erika Unter
>> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
>> Phone: +49-8142-66989-52 Fax: +49-8142-66989-80 Email: hs at denx.de
>>
--
DENX Software Engineering GmbH, Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: +49-8142-66989-52 Fax: +49-8142-66989-80 Email: hs at denx.de
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