Re: [PATCH] cifs: fix bad fids sent over wire

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On 3/21/2022 8:30 AM, Paulo Alcantara wrote:
Tom Talpey <tom@xxxxxxxxxx> writes:

On 3/20/2022 8:20 PM, Paulo Alcantara wrote:
The client used to partially convert the fids to le64, while storing
or sending them by using host endianness.  This broke the client on
big-endian machines.  Instead of converting them to le64, store them
verbatim and then avoid byteswapping when sending them over wire.

Signed-off-by: Paulo Alcantara (SUSE) <pc@xxxxxx>
---
   fs/cifs/smb2misc.c |  4 ++--
   fs/cifs/smb2ops.c  |  8 +++----
   fs/cifs/smb2pdu.c  | 53 ++++++++++++++++++++--------------------------
   3 files changed, 29 insertions(+), 36 deletions(-)

diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
index b25623e3fe3d..3b7c636be377 100644
--- a/fs/cifs/smb2misc.c
+++ b/fs/cifs/smb2misc.c
@@ -832,8 +832,8 @@ smb2_handle_cancelled_mid(struct mid_q_entry *mid, struct TCP_Server_Info *serve
   	rc = __smb2_handle_cancelled_cmd(tcon,
   					 le16_to_cpu(hdr->Command),
   					 le64_to_cpu(hdr->MessageId),
-					 le64_to_cpu(rsp->PersistentFileId),
-					 le64_to_cpu(rsp->VolatileFileId));
+					 rsp->PersistentFileId,
+					 rsp->VolatileFileId);

This conflicts with the statement "store them verbatim". Because the
rsp->{Persistent,Volatile}FileId fields are u64 (integer) types,
they are not being stored verbatim, they are being manipulated
by the CPU load/store instructions. Storing them into a u8[8]
array is more to the point.

Yes, makes sense.

If course, if the rsp structure is purely private to the code, then
the structure element type is similarly private. But a debugger, or
a future structure reference, may once again get it wrong

Are you rejecting the idea of using a byte array?

No.  That would work, too.  I was just trying to avoid changing a lot of
places and eventually making it harder to backport.

I'll go with the byte array then.

If you want to reduce a bit of code change, you could let the
compiler generate the loads and stores via memcpy, with (perhaps)
a struct { u8[8] } instead of the bare array.

Tom.



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