From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Frank Sorenson <sorenson@redhat.com>,
	David Howells <dhowells@redhat.com>,
	Paulo Alcantara <pc@manguebit.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12.y] smb: client: fix reparse buffer bounds in cifs_query_reparse_point()
Date: Tue, 22 Sep 2026 21:39:56 -0400
Message-ID: <20260923013956.878372-1-sashal@kernel.org>
In-Reply-To: <2026092258-electable-undoing-fab9@gregkh>
References: <2026092258-electable-undoing-fab9@gregkh>
Precedence: bulk
MIME-Version: 1.0
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From: Frank Sorenson <sorenson@redhat.com>

[ Upstream commit 5f0306e731e2f46e91419eae57eee3a241c055e0 ]

In cifs_query_reparse_point(), the start >= end check before casting to
struct reparse_data_buffer * only ensures the start pointer is within the
response. It fails to verify that there is enough space remaining for the
fixed 8-byte header of the structure.

If a server provides a DataOffset that leaves less than 8 bytes remaining,
the check passes, but subsequent reads of ReparseTag and ReparseDataLength
will occur out-of-bounds.

Fix this by ensuring the remaining space is at least the size of the
reparse_data_buffer structure before accessing its fields.

Fixes: 56e84c64fc25 ("cifs: Fix validation of SMB1 query reparse point response")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
[ Adjusted context to retain existing `rc = -EIO` error handling instead of upstream `smb_EIO2()`. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/client/cifssmb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index 01c78d9e7ec0e..df02e2d9204ab 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -2829,7 +2829,7 @@ int cifs_query_reparse_point(const unsigned int xid,
 
 	end = 2 + get_bcc(&io_rsp->hdr) + (__u8 *)&io_rsp->ByteCount;
 	start = (__u8 *)&io_rsp->hdr.Protocol + data_offset;
-	if (start >= end) {
+	if (start >= end || (size_t)(end - start) < sizeof(*buf)) {
 		rc = -EIO;
 		goto error;
 	}
-- 
2.53.0