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

Alexander Lochmann
2019-01-11T15:42:31Z

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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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