[PATCH][next] tls: Avoid -Wflex-array-member-not-at-end warning

[PATCH][next] tls: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the new TRAILING_OVERLAP() helper to fix the following warning:

net/tls/tls.h:131:29: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM)
and a set of members that would otherwise follow it. This overlays
the trailing members onto the FAM while preserving the original
memory layout.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 net/tls/tls.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/tls/tls.h b/net/tls/tls.h
index 4e077068e6d9..d06435d186c0 100644
--- a/net/tls/tls.h
+++ b/net/tls/tls.h
@@ -128,8 +128,9 @@ struct tls_rec {
 
 	char aad_space[TLS_AAD_SPACE_SIZE];
 	u8 iv_data[TLS_MAX_IV_SIZE];
-	struct aead_request aead_req;
-	u8 aead_req_ctx[];
+	TRAILING_OVERLAP(struct aead_request, aead_req, __ctx,
+		u8 aead_req_ctx[];
+	);
 };
 
 int __net_init tls_proc_init(struct net *net);
-- 
2.43.0

Re: [PATCH][next] tls: Avoid -Wflex-array-member-not-at-end warning

[Sabrina Dubroca]

2025-09-22, 16:39:20 +0200, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the new TRAILING_OVERLAP() helper to fix the following warning:
> 
> net/tls/tls.h:131:29: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> This helper creates a union between a flexible-array member (FAM)
> and a set of members that would otherwise follow it. This overlays
> the trailing members onto the FAM while preserving the original
> memory layout.

Do we need to keep aead_req_ctx in tls_rec? It doesn't seem to be
used, and I don't see it ever being used since it was introduced in
commit a42055e8d2c3 ("net/tls: Add support for async encryption of
records for performance").

-- 
Sabrina

Re: [PATCH][next] tls: Avoid -Wflex-array-member-not-at-end warning

[Sabrina Dubroca]

2025-09-23, 11:37:55 +0200, Gustavo A. R. Silva wrote:
> 
> 
> On 9/22/25 17:21, Sabrina Dubroca wrote:
> > 2025-09-22, 16:39:20 +0200, Gustavo A. R. Silva wrote:
> > > -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> > > getting ready to enable it, globally.
> > > 
> > > Use the new TRAILING_OVERLAP() helper to fix the following warning:
> > > 
> > > net/tls/tls.h:131:29: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > > 
> > > This helper creates a union between a flexible-array member (FAM)
> > > and a set of members that would otherwise follow it. This overlays
> > > the trailing members onto the FAM while preserving the original
> > > memory layout.
> > 
> > Do we need to keep aead_req_ctx in tls_rec? It doesn't seem to be
> > used, and I don't see it ever being used since it was introduced in
> > commit a42055e8d2c3 ("net/tls: Add support for async encryption of
> > records for performance").
> 
> If this (flex array) is not going to be needed in the future, I'm
> happy to remove it. :)

I don't see what we'd use it for, aead_request.__ctx contains private
data from the crypto code (all accesses seem to be through
aead_request_ctx defined in include/crypto/internal/aead.h, see also
the kdoc: "Start of private context data").
And we haven't seen the author of a42055e8d2c3 in a while, so we can't
ask about the intention behind this field.

So IMO, tls_rec.aead_req_ctx can simply go away. Would you send the
patch?

-- 
Sabrina

Re: [PATCH][next] tls: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

>>
>> If this (flex array) is not going to be needed in the future, I'm
>> happy to remove it. :)
> 
> I don't see what we'd use it for, aead_request.__ctx contains private
> data from the crypto code (all accesses seem to be through
> aead_request_ctx defined in include/crypto/internal/aead.h, see also
> the kdoc: "Start of private context data").
> And we haven't seen the author of a42055e8d2c3 in a while, so we can't
> ask about the intention behind this field.
> 
> So IMO, tls_rec.aead_req_ctx can simply go away. Would you send the
> patch?
> 

Done: https://lore.kernel.org/linux-hardening/aNMG1lyXw4XEAVaE@kspp/

Thank you for the feedback. :)

-Gustavo