Subject: FAILED: patch "[PATCH] smb: client: reject short READ responses in CIFSSMBRead()" failed to apply to 5.10-stable tree
To: diego@bynar.io,dhowells@redhat.com,pc@manguebit.org
Cc: <stable@vger.kernel.org>
From: <gregkh@linuxfoundation.org>
Date: Wed, 16 Sep 2026 17:40:06 +0100
Message-ID: <2026091606-quickstep-handstand-fba1@gregkh>
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The patch below does not apply to the 5.10-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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x e6142a8bfc230c7263eb8b0475249c958ce49367
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026091606-quickstep-handstand-fba1@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:


thanks,

greg k-h

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

From e6142a8bfc230c7263eb8b0475249c958ce49367 Mon Sep 17 00:00:00 2001
From: Diego Oliva <diego@bynar.io>
Date: Wed, 2 Sep 2026 11:42:06 +0100
Subject: [PATCH] smb: client: reject short READ responses in CIFSSMBRead()

CIFSSMBRead() reads DataLengthHigh, DataLength and DataOffset out of
the READ_RSP returned by the server without first checking that a
whole READ_RSP was actually received. The length of the response is
recorded in rsp_iov.iov_len, but nothing constrains it to be at least
read_rsp_size before those fields are dereferenced.

A malicious or compromised SMB1 server can return a response shorter
than the READ_RSP header, so that parsing the header itself reads past
the end of the receive buffer. SMB1 is not negotiated by default;
reaching this code requires an explicit vers=1.0 mount.

Reject the response unless it is at least read_rsp_size bytes long.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Paulo Alcantara <pc@manguebit.org>
Cc: stable@vger.kernel.org # 6.19.x
Assisted-by: Bynario AI
Signed-off-by: Diego Oliva <diego@bynar.io>
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index f8aa9e7b4bc6..be13ab37039d 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1719,6 +1719,14 @@ CIFSSMBRead(const unsigned int xid, struct cifs_io_parms *io_parms,
 	pSMBr = (READ_RSP *)rsp_iov.iov_base;
 	if (rc) {
 		cifs_dbg(VFS, "Send error in read = %d\n", rc);
+	} else if (rsp_iov.iov_len < tcon->ses->server->vals->read_rsp_size) {
+		/* check that the received response can hold a whole READ_RSP */
+		cifs_dbg(FYI, "%s: server returned short header. got=%zu expected=%zu\n",
+			 __func__, rsp_iov.iov_len,
+			 tcon->ses->server->vals->read_rsp_size);
+		rc = smb_EIO2(smb_eio_trace_read_rsp_short,
+			      rsp_iov.iov_len, tcon->ses->server->vals->read_rsp_size);
+		*nbytes = 0;
 	} else {
 		int data_length = le16_to_cpu(pSMBr->DataLengthHigh);
 		data_length = data_length << 16;