Re: [PATCH] Abort file_remove_privs() for non-reg. files

Alexander Lochmann
2019-03-08T15:10:32Z

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Hello Al,

Meanwhile, have you had the opportunity to review our patch?

Regards,
Alex

On 11.01.19 16:42, Alexander Lochmann wrote:
> Hello Al,
>
> Have you had the opportunity to review our patch?
>
> Cheers,
> Alex
>
> On 17.12.18 09:28, Jan Kara wrote:
>> On Fri 14-12-18 11:55:52, Alexander Lochmann wrote:
>>>
>>> file_remove_privs() might be called for non-regular files, e.g.
>>> blkdev inode. There is no reason to do its job on things
>>> like blkdev inodes, pipes, or cdevs. Hence, abort if
>>> file does not refer to a regular inode.
>>> The following stacktrace shows how to get there:
>>> 13: entry_SYSENTER_32:460
>>> 12: do_fast_syscall_32:410
>>> 11: _static_cpu_has:146
>>> 10: do_syscall_32_irqs_on:322
>>> 09: SyS_pwrite64:636
>>> 08: SYSC_pwrite64:650
>>> 07: fdput:38
>>> 06: vfs_write:560
>>> 05: __vfs_write:512
>>> 04: new_sync_write:500
>>> 03: blkdev_write_iter:1977
>>> 02: __generic_file_write_iter:2897
>>> 01: file_remove_privs:1818
>>> 00: inode_has_no_xattr:3163
>>>
>>> Found by LockDoc (Alexander Lochmann, Horst Schirmeier and Olaf
>>> Spinczyk)
>>>
>>> Signed-off-by: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
>>> Signed-off-by: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>
>>
>> The patch looks good to me. You can add:
>>
>> Reviewed-by: Jan Kara <jack@suse.cz>
>>
>> Honza
>>
>>> ---
>>> fs/inode.c | 9 +++++++--
>>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/inode.c b/fs/inode.c
>>> index 35d2108d567c..682088190413 100644
>>> --- a/fs/inode.c
>>> +++ b/fs/inode.c
>>> @@ -1820,8 +1820,13 @@ int file_remove_privs(struct file *file)
>>> int kill;
>>> int error = 0;
>>>
>>> - /* Fast path for nothing security related */
>>> - if (IS_NOSEC(inode))
>>> + /*
>>> + * Fast path for nothing security related.
>>> + * As well for non-regular files, e.g. blkdev inodes.
>>> + * For example, blkdev_write_iter() might get here
>>> + * trying to remove privs which it is not allowed to.
>>> + */
>>> + if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
>>> return 0;
>>>
>>> kill = dentry_needs_remove_privs(dentry);
>>> --
>>> 2.19.2
>>>
>>
>>
>>
>

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