linux-kernel - [PATCH 3.16 117/346] CIFS: Fix a possible invalid memory access in smb2_query

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Message-ID: <lsq.1479082460.219230533@decadent.org.uk>
Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Steve French" <smfrench@...il.com>,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        "Pavel Shilovsky" <pshilovsky@...ba.org>
Subject: [PATCH 3.16 117/346] CIFS: Fix a possible invalid memory access
 in smb2_query_symlink()

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Pavel Shilovsky <pshilovsky@...ba.org>

commit 7893242e2465aea6f2cbc2639da8fa5ce96e8cc2 upstream.

During following a symbolic link we received err_buf from SMB2_open().
While the validity of SMB2 error response is checked previously
in smb2_check_message() a symbolic link payload is not checked at all.
Fix it by adding such checks.

Cc: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Pavel Shilovsky <pshilovsky@...ba.org>
Signed-off-by: Steve French <smfrench@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/cifs/smb2ops.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -858,6 +858,9 @@ smb2_new_lease_key(struct cifs_fid *fid)
 	get_random_bytes(fid->lease_key, SMB2_LEASE_KEY_SIZE);
 }
 
+#define SMB2_SYMLINK_STRUCT_SIZE \
+	(sizeof(struct smb2_err_rsp) - 1 + sizeof(struct smb2_symlink_err_rsp))
+
 static int
 smb2_query_symlink(const unsigned int xid, struct cifs_tcon *tcon,
 		   const char *full_path, char **target_path,
@@ -870,7 +873,10 @@ smb2_query_symlink(const unsigned int xi
 	struct cifs_fid fid;
 	struct smb2_err_rsp *err_buf = NULL;
 	struct smb2_symlink_err_rsp *symlink;
-	unsigned int sub_len, sub_offset;
+	unsigned int sub_len;
+	unsigned int sub_offset;
+	unsigned int print_len;
+	unsigned int print_offset;
 
 	cifs_dbg(FYI, "%s: path: %s\n", __func__, full_path);
 
@@ -891,11 +897,33 @@ smb2_query_symlink(const unsigned int xi
 		kfree(utf16_path);
 		return -ENOENT;
 	}
+
+	if (le32_to_cpu(err_buf->ByteCount) < sizeof(struct smb2_symlink_err_rsp) ||
+	    get_rfc1002_length(err_buf) + 4 < SMB2_SYMLINK_STRUCT_SIZE) {
+		kfree(utf16_path);
+		return -ENOENT;
+	}
+
 	/* open must fail on symlink - reset rc */
 	rc = 0;
 	symlink = (struct smb2_symlink_err_rsp *)err_buf->ErrorData;
 	sub_len = le16_to_cpu(symlink->SubstituteNameLength);
 	sub_offset = le16_to_cpu(symlink->SubstituteNameOffset);
+	print_len = le16_to_cpu(symlink->PrintNameLength);
+	print_offset = le16_to_cpu(symlink->PrintNameOffset);
+
+	if (get_rfc1002_length(err_buf) + 4 <
+			SMB2_SYMLINK_STRUCT_SIZE + sub_offset + sub_len) {
+		kfree(utf16_path);
+		return -ENOENT;
+	}
+
+	if (get_rfc1002_length(err_buf) + 4 <
+			SMB2_SYMLINK_STRUCT_SIZE + print_offset + print_len) {
+		kfree(utf16_path);
+		return -ENOENT;
+	}
+
 	*target_path = cifs_strndup_from_utf16(
 				(char *)symlink->PathBuffer + sub_offset,
 				sub_len, true, cifs_sb->local_nls);