Re: [PATCH 1/2] ksmbd: skip metadata-only opens in sharing checks

[Ian Bridges <icb@fastmail.org>]

Hi Namjae,

You're right. With this patch a CREATE for READ_CONTROL with
FILE_OVERWRITE or FILE_SUPERSEDE skips the sharing check, and
smb2_open() then truncates the file. In your example, with an existing
FILE_READ_DATA open at ShareAccess 0, the second CREATE for
READ_CONTROL and FILE_OVERWRITE at ShareAccess 0 succeeds and the
file's data is lost. A test that runs smb2_open() confirms it.

I'll send a v2 that does what you suggest: the sharing check counts an
open that truncates the file as holding FILE_WRITE_DATA, and the
returned handle keeps the open's own access. An open of a directory or
a named stream, or one for attributes only, gets O_TRUNC but is not
truncated, so it is not counted.

A truncating open is already on the inode's open list before it
truncates, so v2 also counts it as holding FILE_WRITE_DATA, for as long
as it is open, when deciding whether a later open is checked against
it. Patch 2 does not change.

Thanks,
Ian