FAILED: patch "[PATCH] smb: smbdirect: fix buffer length underflow in RDMA transfers" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] smb: smbdirect: fix buffer length underflow in RDMA transfers" failed to apply to 6.6-stable tree

[gregkh]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 7193241a49c958782ba4b8df06da3734d1e317d2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110437-flagpole-glitch-eff0@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7193241a49c958782ba4b8df06da3734d1e317d2 Mon Sep 17 00:00:00 2001
From: Stefan Metzmacher <metze@samba.org>
Date: Fri, 23 Oct 2026 19:26:09 +0900
Subject: [PATCH] smb: smbdirect: fix buffer length underflow in RDMA transfers

When a remote buffer descriptor is larger than the remaining local
buffer, smbdirect_connection_rdma_xmit() clamps its length and sets
buf_len to zero. The common accounting code then subtracts the clamped
length from buf_len, causing it to underflow. If another descriptor
follows, the loop processes it with a wrapped remaining length and
includes memory beyond the local buffer in the RDMA transfer.

A client can trigger an out-of-bounds kernel write with an SMB WRITE
request, or an out-of-bounds kernel read with an SMB READ request, by
supplying multiple RDMA buffer descriptors with an oversized descriptor
before the last one.

Remove the premature assignment to buf_len. Subtracting the clamped length
already consumes the remaining buffer, so the next iteration stops and
only descriptors within the local buffer are used to build work requests.

Fixes: e628bf939aaf ("ksmbd: reduce descriptor size if remaining bytes is less than request size")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-33549
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

diff --git a/fs/smb/smbdirect/rw.c b/fs/smb/smbdirect/rw.c
index 6fe38042cfb9..cb142c3c50b2 100644
--- a/fs/smb/smbdirect/rw.c
+++ b/fs/smb/smbdirect/rw.c
@@ -143,7 +143,6 @@ int smbdirect_connection_rdma_xmit(struct smbdirect_socket *sc,
 		if (desc_buf_len > buf_len) {
 			desc_buf_len = buf_len;
 			desc[i].length = cpu_to_le32(desc_buf_len);
-			buf_len = 0;
 		}
 
 		credits_needed += smbdirect_connection_calc_rw_credits(sc,

Re: FAILED: patch "[PATCH] smb: smbdirect: fix buffer length underflow in RDMA transfers" failed to apply to 6.6-stable tree

[Stefan Metzmacher]

[-- Attachment #1: Type: text/plain, Size: 2799 bytes --]

Am 04.11.26 um 19:29 schrieb gregkh@linuxfoundation.org:
> 
> The patch below does not apply to the 6.6-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
> git checkout FETCH_HEAD
> git cherry-pick -x 7193241a49c958782ba4b8df06da3734d1e317d2
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110437-flagpole-glitch-eff0@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'
> 
> Possible dependencies:
> 
> 
> 
> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
>  From 7193241a49c958782ba4b8df06da3734d1e317d2 Mon Sep 17 00:00:00 2001
> From: Stefan Metzmacher <metze@samba.org>
> Date: Fri, 23 Oct 2026 19:26:09 +0900
> Subject: [PATCH] smb: smbdirect: fix buffer length underflow in RDMA transfers
> 
> When a remote buffer descriptor is larger than the remaining local
> buffer, smbdirect_connection_rdma_xmit() clamps its length and sets
> buf_len to zero. The common accounting code then subtracts the clamped
> length from buf_len, causing it to underflow. If another descriptor
> follows, the loop processes it with a wrapped remaining length and
> includes memory beyond the local buffer in the RDMA transfer.
> 
> A client can trigger an out-of-bounds kernel write with an SMB WRITE
> request, or an out-of-bounds kernel read with an SMB READ request, by
> supplying multiple RDMA buffer descriptors with an oversized descriptor
> before the last one.
> 
> Remove the premature assignment to buf_len. Subtracting the clamped length
> already consumes the remaining buffer, so the next iteration stops and
> only descriptors within the local buffer are used to build work requests.
> 
> Fixes: e628bf939aaf ("ksmbd: reduce descriptor size if remaining bytes is less than request size")
> Cc: stable@vger.kernel.org
> Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-33549
> Signed-off-by: Stefan Metzmacher <metze@samba.org>
> Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
> 
> diff --git a/fs/smb/smbdirect/rw.c b/fs/smb/smbdirect/rw.c
> index 6fe38042cfb9..cb142c3c50b2 100644
> --- a/fs/smb/smbdirect/rw.c
> +++ b/fs/smb/smbdirect/rw.c
> @@ -143,7 +143,6 @@ int smbdirect_connection_rdma_xmit(struct smbdirect_socket *sc,
>   		if (desc_buf_len > buf_len) {
>   			desc_buf_len = buf_len;
>   			desc[i].length = cpu_to_le32(desc_buf_len);
> -			buf_len = 0;
>   		}
>   
>   		credits_needed += smbdirect_connection_calc_rw_credits(sc,

[-- Attachment #2: backport-6.6-smbdirect-rdma-xmit-underflow.txt --]
[-- Type: text/plain, Size: 2132 bytes --]

From 16f935810fc6553d2caff4bd740e21e3dc0ae40a Mon Sep 17 00:00:00 2001
From: Stefan Metzmacher <metze@samba.org>
Date: Fri, 23 Oct 2026 19:26:09 +0900
Subject: [PATCH 6.6.y] smb: smbdirect: fix buffer length underflow in RDMA
 transfers

[ Upstream commit 7193241a49c958782ba4b8df06da3734d1e317d2 ]

When a remote buffer descriptor is larger than the remaining local
buffer, smbdirect_connection_rdma_xmit() clamps its length and sets
buf_len to zero. The common accounting code then subtracts the clamped
length from buf_len, causing it to underflow. If another descriptor
follows, the loop processes it with a wrapped remaining length and
includes memory beyond the local buffer in the RDMA transfer.

A client can trigger an out-of-bounds kernel write with an SMB WRITE
request, or an out-of-bounds kernel read with an SMB READ request, by
supplying multiple RDMA buffer descriptors with an oversized descriptor
before the last one.

Remove the premature assignment to buf_len. Subtracting the clamped length
already consumes the remaining buffer, so the next iteration stops and
only descriptors within the local buffer are used to build work requests.

Fixes: e628bf939aaf ("ksmbd: reduce descriptor size if remaining bytes is less than request size")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-33549
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
[ metze: in 6.6 the code is smb_direct_rdma_xmit() in
  fs/smb/server/transport_rdma.c ]
Assisted-by: Claude:claude-opus-5-5
---
 fs/smb/server/transport_rdma.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/smb/server/transport_rdma.c b/fs/smb/server/transport_rdma.c
index d522ace20840..60c03e590ba9 100644
--- a/fs/smb/server/transport_rdma.c
+++ b/fs/smb/server/transport_rdma.c
@@ -1388,7 +1388,6 @@ static int smb_direct_rdma_xmit(struct smb_direct_transport *t,
 		if (desc_buf_len > buf_len) {
 			desc_buf_len = buf_len;
 			desc[i].length = cpu_to_le32(desc_buf_len);
-			buf_len = 0;
 		}
 
 		credits_needed += calc_rw_credits(t, desc_buf, desc_buf_len);
-- 
2.53.0

[PATCH 6.6.y] smb: smbdirect: fix buffer length underflow in RDMA transfers

[Sasha Levin]

From: Stefan Metzmacher <metze@samba.org>

[ Upstream commit 7193241a49c958782ba4b8df06da3734d1e317d2 ]

When a remote buffer descriptor is larger than the remaining local
buffer, smbdirect_connection_rdma_xmit() clamps its length and sets
buf_len to zero. The common accounting code then subtracts the clamped
length from buf_len, causing it to underflow. If another descriptor
follows, the loop processes it with a wrapped remaining length and
includes memory beyond the local buffer in the RDMA transfer.

A client can trigger an out-of-bounds kernel write with an SMB WRITE
request, or an out-of-bounds kernel read with an SMB READ request, by
supplying multiple RDMA buffer descriptors with an oversized descriptor
before the last one.

Remove the premature assignment to buf_len. Subtracting the clamped length
already consumes the remaining buffer, so the next iteration stops and
only descriptors within the local buffer are used to build work requests.

Fixes: e628bf939aaf ("ksmbd: reduce descriptor size if remaining bytes is less than request size")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-33549
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
[ sashal: adjusted context to apply the change in smb_direct_rdma_xmit() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/server/transport_rdma.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/smb/server/transport_rdma.c b/fs/smb/server/transport_rdma.c
index 8987b1167a38c..5178c7443ebb7 100644
--- a/fs/smb/server/transport_rdma.c
+++ b/fs/smb/server/transport_rdma.c
@@ -1388,7 +1388,6 @@ static int smb_direct_rdma_xmit(struct smb_direct_transport *t,
 		if (desc_buf_len > buf_len) {
 			desc_buf_len = buf_len;
 			desc[i].length = cpu_to_le32(desc_buf_len);
-			buf_len = 0;
 		}
 
 		credits_needed += calc_rw_credits(t, desc_buf, desc_buf_len);
-- 
2.53.0

Re: FAILED: patch "[PATCH] smb: smbdirect: fix buffer length underflow in RDMA transfers" failed to apply to 6.6-stable tree

[Sasha Levin]

> smb: smbdirect: fix buffer length underflow in RDMA transfers

Queued your backport for 6.6, thanks.

-- 
Thanks,
Sasha