Re: [PATCH net v5 1/1] net: openvswitch: reallocate update replies for mismatched IDs

On 8/3/26 2:29 AM, Zhiling Zou wrote:
> ovs_flow_cmd_new() preallocates the optional reply skb before it takes
> ovs_mutex and before it knows which existing flow will be updated.
> 
> That is normally fine because the skb is sized from the request flow
> identifier.  That identifier also becomes the inserted flow's identifier.
> For updates, however, a request with a UFID may miss the UFID lookup and
> then fall back to the flow key lookup.  That lookup can legitimately find
> an existing key-identified flow.  UFIDs are optional and the flow key is
> the primary identifier.
> 
> For echoed replies, ovs_flow_cmd_fill_info() writes the matched flow's
> identifier, not the request identifier used for the preallocation.  A short
> request UFID can therefore leave too little room for the key identifier.
> The fill can then fail with -EMSGSIZE and hit the BUG_ON(error < 0) in the
> update path.
> 
> Once the update target has been resolved, reallocate the reply skb if the
> matched flow needs a larger reply than the request identifier allowed.  Do
> this before replacing the actions so the request can still fail cleanly if
> the rare extra allocation fails.
> 
> Fixes: 74ed7ab9264c ("openvswitch: Add support for unique flow IDs.")
> Cc: [email protected]
> Reported-by: Vega <[email protected]>
> Signed-off-by: Zhiling Zou <[email protected]>
> ---
> changes in v5:
> - Rename current and desired to cur and req to avoid the kernel current macro.
> - Split the ovs_flow_cmd_alloc_info() call so no added line exceeds 80 columns.
> - v4 Link: https://lore.kernel.org/all/3b76cbe50252a5650c3b69c789ed36481d0bbee4.1785583308.git.zhilinz-bq61tP5cpwQREpMHaJNmVQ@public.gmane.org/

Reviewed-by: Ilya Maximets <[email protected]>