[PATCH 5.10.y] smb: client: bound POSIX lock data area by response length

[Sasha Levin <sashal@kernel.org>]

From: Ratnaker Gautam <ratnaker.gautam@kuleuven.be>

[ Upstream commit 8fc9af68c57156ff64769f30e831553cd03b3000 ]

CIFSSMBPosixLock() receives a TRANS2 response whose server-provided
DataOffset and DataCount are not required by validate_t2() to describe an
interval inside the response. A server can therefore make the client read a
cifs_posix_lock beyond the response buffer and return those kernel bytes
through F_GETLK.

Use smbCalcSize() to obtain the full response length after any multipart
TRANS2 reassembly, then reject data areas that extend past it before
dereferencing them.

Fixes: fc94cdb94462 ("[CIFS] Fix new POSIX Locking for setting lock_type correctly on unlock")
Reported-by: Ratnaker Gautam <ratnaker.gautam@kuleuven.be>
Cc: stable@vger.kernel.org
Signed-off-by: Ratnaker Gautam <ratnaker.gautam@kuleuven.be>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
[ sashal: adjusted response validation to subtract the 4-byte header from smbCalcSize() and use plain -EIO instead of traced errors ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/cifs/cifssmb.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 67ff1669cab2a..08ae1d7d2c516 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -2592,6 +2592,7 @@ CIFSSMBPosixLock(const unsigned int xid, struct cifs_tcon *tcon,
 		cifs_dbg(FYI, "Send error in Posix Lock = %d\n", rc);
 	} else if (pLockData) {
 		/* lock structure can be returned on get */
+		unsigned int rsp_len;
 		__u16 data_offset;
 		__u16 data_count;
 		rc = validate_t2((struct smb_t2_rsp *)pSMBr);
@@ -2602,10 +2603,16 @@ CIFSSMBPosixLock(const unsigned int xid, struct cifs_tcon *tcon,
 		}
 		data_offset = le16_to_cpu(pSMBr->t2.DataOffset);
 		data_count  = le16_to_cpu(pSMBr->t2.DataCount);
+		rsp_len = smbCalcSize(&pSMBr->hdr) - 4;
 		if (data_count < sizeof(struct cifs_posix_lock)) {
 			rc = -EIO;
 			goto plk_err_exit;
 		}
+		if (data_offset > rsp_len ||
+		    data_count > rsp_len - data_offset) {
+			rc = -EIO;
+			goto plk_err_exit;
+		}
 		parm_data = (struct cifs_posix_lock *)
 			((char *)&pSMBr->hdr.Protocol + data_offset);
 		if (parm_data->lock_type == cpu_to_le16(CIFS_UNLCK))
-- 
2.53.0