[PATCH v3] ksmbd: fill in FileSysIdentifier in FS_POSIX_INFORMATION

[Aleksandr Khromov <haa@amicon.ru>]

smb2_get_info_filesystem() reports 56 bytes for FS_POSIX_INFORMATION,
that is the whole of FILE_SYSTEM_POSIX_INFO, but never assigns
FileSysIdentifier.  Those eight bytes go to the client as they are found
in the response buffer.

The buffer is zeroed on allocation, so a standalone request leaks
nothing.  A compound request can leak: the offset of the next response
is advanced by the length pinned for the previous one, so a reply that
was written into the buffer and then dropped in favour of the short
error response of smb2_set_err_rsp() stays there, and the next reply is
laid over it with only the header cleared.

Report the file system id statfs() returned, which is what the field is
for.  FileSysIdentifier is __le64 and f_fsid is a pair of ints, so
assemble the value first, val[0] as the low half, and convert it on the
way out.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Signed-off-by: Aleksandr Khromov <haa@amicon.ru>
---
v3: FileSysIdentifier is __le64, so assemble the value and convert it
    instead of memcpy()ing the host representation of f_fsid into the
    field (Namjae Jeon).  Patches 1/3 and 2/3 of v2 were applied to
    ksmbd-for-next, so this is the only one left of the series.
v2: https://lore.kernel.org/linux-cifs/20260824102248.178152-4-haa@amicon.ru/

 fs/smb/server/smb2pdu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 5e83ad4f085e..a5771474b2af 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -6167,6 +6167,9 @@ static int smb2_get_info_filesystem(struct ksmbd_work *work,
 			info->UserBlocksAvail = cpu_to_le64(stfs.f_bavail);
 			info->TotalFileNodes = cpu_to_le64(stfs.f_files);
 			info->FreeFileNodes = cpu_to_le64(stfs.f_ffree);
+			info->FileSysIdentifier =
+				cpu_to_le64((u64)(u32)stfs.f_fsid.val[1] << 32 |
+					    (u32)stfs.f_fsid.val[0]);
 			rsp->OutputBufferLength = cpu_to_le32(56);
 		}
 		break;
-- 
2.48.1