[LTP] [PATCH] runtest/fs: Don't read files in /dev indiscriminately

[Punit Agrawal]

Hi Richard,

Richard Palethorpe <rpalethorpe@suse.de> writes:

> Hello,
>
> Punit Agrawal writes:
>
>> read_all_dev attempts to read 1024 bytes from all devices in /dev. As
>> nodes in /dev represent devices, any access can have side-effects -
>> sometimes fatally so, e.g., accessing /dev/port on Juno R2 and AMD
>> Seattle lead to synchronous external abort or SError (system error)
>> interrupt depending on the access pattern.
>>
>> There isn't much the kernel can do about the aborts other than panic
>> the system.
>>
>> The side-effects problem is also highlighted by the recent exclusion
>> added for watchdog devices. See commit 4a41aa6b48c134e ("runtest/fs:
>> filter /dev/watchdog* for read_all_dev by default").
>>
>> It would be better to replace indiscriminate reading of /dev files
>> with tests targeting specific files in /dev which have defined known
>> behaviour, e.g., /dev/null, /dev/urandom, etc.
>>
>> In the meanwhile, drop the indiscriminate reading of files in /dev.
>
> Another solution might be to add an option which drops privileges before
> running the test on /dev. An unprivileged user should not have access to files
> like /dev/port, but will for /dev/null and /dev/urandom.

The following files have unprivileged read permission in /dev -

vfio/vfio
net/tun
ptmx
tty
urandom
random
full
zero
null

which seems a reasonable set (this'll likely vary by system).

So dropping privileges should keep things ticking.

Thanks,
Punit


>
>>
>> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
>> Cc: xuyang.jy@cn.fujitsu.com
>> Cc: naresh.kamboju@linaro.org
>> Cc: rpalethorpe@suse.com
>> Cc: chrubis@suse.cz
>> Cc: james.morse@arm.com
>> ---
>> Hi,
>>
>> The test leads to panic during nightly ltp runs on internal
>> systems. Looking at the crash report from Naresh[0], it looks likely
>> that he's facing the same problem.
>>
>> Please consider including in upcoming release.
>>
>> Thanks,
>> Punit
>>
>> [0] http://lists.linux.it/pipermail/ltp/2018-May/007954.html
>> ---
>>  runtest/fs | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/runtest/fs b/runtest/fs
>> index 42a9bfcbf..c7ed64fbf 100644
>> --- a/runtest/fs
>> +++ b/runtest/fs
>> @@ -69,7 +69,6 @@ fs_di fs_di -d $TMPDIR
>>  # Was not sure why it should reside in runtest/crashme and won´t get tested ever
>>  proc01 proc01 -m 128
>>
>> -read_all_dev read_all -d /dev -e '/dev/watchdog?(0)' -q -r 10
>>  read_all_proc read_all -d /proc -q -r 10
>>  read_all_sys read_all -d /sys -q -r 10
>
>
> --
> Thank you,
> Richard.