[PATCH 5/7] smb: client: reject FIND data areas that run past the received response

[Diego Oliva <diego@bynar.io>]

CIFSFindFirst() and CIFSFindNext() take the directory entries of a
TRANS2_FIND_FIRST2 or TRANS2_FIND_NEXT2 response from DataOffset for
DataCount bytes. validate_t2() bounds DataOffset at 1024 and
ParameterCount + DataCount by the byte count, and nothing compares
DataOffset + DataCount with the number of bytes SendReceive() copied
into the buffer.

smb_init() places the request and the response in the same
cifs_request allocation and cifs_buf_get() clears only the start of
it, so a short response whose data area extends past its end has
srch_entries_start point at bytes of the request that was just sent,
or at whatever the allocation held before, and those bytes are parsed
as directory entries. cifs_readdir() and find_cifs_entry() walk the
entries with nxt_dir_entry(), which checks every entry but the first
of a response against the end of the SMB; cifs_query_path_info() and
cifs_backup_query_path_info() read the first entry with no check at
all. Those reads stay inside the allocation, but what they return is
not part of the response. The last entry, which LastNameOffset locates
relative to the data area, is bounded against the received response
by an earlier patch of this series, as is every entry that
cifs_fill_dirent() parses; the walk itself and the two query functions
are not.

SMB1 is not negotiated by default; reaching this code requires an
explicit vers=1.0 mount.

Reject a response whose data area extends past the received length,
with the -EINVAL that validate_t2() returns for the other malformed
transaction responses. cifs_query_path_info() and
cifs_backup_query_path_info() still read a whole entry from a data
area that may be smaller than one; that is not changed here.

A conforming server is not affected. The data block of a transaction
response is part of the SMB, so DataOffset + DataCount cannot exceed
the smbCalcSize() bytes that SendReceive() copies; coalesce_t2()
appends each secondary response to the data area and adds its length
to both DataCount and the byte count, which keeps that relation.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: <stable@vger.kernel.org>
Assisted-by: Bynario AI
Signed-off-by: Diego Oliva <diego@bynar.io>
---
 fs/smb/client/cifssmb.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index 7eb83dd737fc..107ca76e53d1 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -4412,6 +4412,7 @@ CIFSFindFirst(const unsigned int xid, struct cifs_tcon *tcon,
 	TRANSACTION2_FFIRST_RSP *pSMBr = NULL;
 	T2_FFIRST_RSP_PARMS *parms;
 	struct nls_table *nls_codepage;
+	unsigned int data_off, data_count;
 	unsigned int in_len, lnoff;
 	__u16 params, byte_count;
 	int bytes_returned = 0;
@@ -4530,11 +4531,19 @@ CIFSFindFirst(const unsigned int xid, struct cifs_tcon *tcon,
 		return rc;
 	}
 
+	data_off = le16_to_cpu(pSMBr->t2.DataOffset);
+	data_count = le16_to_cpu(pSMBr->t2.DataCount);
+	if (data_off + data_count > (unsigned int)bytes_returned) {
+		cifs_dbg(VFS, "%s: data area offset %u count %u past response length %d\n",
+			 __func__, data_off, data_count, bytes_returned);
+		cifs_buf_release(pSMB);
+		return -EINVAL;
+	}
+
 	psrch_inf->unicode = !!(pSMBr->hdr.Flags2 & SMBFLG2_UNICODE);
 	psrch_inf->ntwrk_buf_start = (char *)pSMBr;
 	psrch_inf->smallBuf = false;
-	psrch_inf->srch_entries_start = (char *)&pSMBr->hdr.Protocol +
-		le16_to_cpu(pSMBr->t2.DataOffset);
+	psrch_inf->srch_entries_start = (char *)&pSMBr->hdr.Protocol + data_off;
 
 	parms = (T2_FFIRST_RSP_PARMS *)((char *)&pSMBr->hdr.Protocol +
 					le16_to_cpu(pSMBr->t2.ParameterOffset));
@@ -4568,6 +4577,7 @@ int CIFSFindNext(const unsigned int xid, struct cifs_tcon *tcon,
 	TRANSACTION2_FNEXT_REQ *pSMB = NULL;
 	TRANSACTION2_FNEXT_RSP *pSMBr = NULL;
 	T2_FNEXT_RSP_PARMS *parms;
+	unsigned int data_off, data_count;
 	unsigned int name_len, in_len;
 	unsigned int lnoff;
 	__u16 params, byte_count;
@@ -4650,13 +4660,22 @@ int CIFSFindNext(const unsigned int xid, struct cifs_tcon *tcon,
 		cifs_buf_release(pSMB);
 		return rc;
 	}
+
+	data_off = le16_to_cpu(pSMBr->t2.DataOffset);
+	data_count = le16_to_cpu(pSMBr->t2.DataCount);
+	if (data_off + data_count > (unsigned int)bytes_returned) {
+		cifs_dbg(VFS, "%s: data area offset %u count %u past response length %d\n",
+			 __func__, data_off, data_count, bytes_returned);
+		cifs_buf_release(pSMB);
+		return -EINVAL;
+	}
+
 	/* BB fixme add lock for file (srch_info) struct here */
 	psrch_inf->unicode = !!(pSMBr->hdr.Flags2 & SMBFLG2_UNICODE);
 	response_data = (char *)&pSMBr->hdr.Protocol +
 		le16_to_cpu(pSMBr->t2.ParameterOffset);
 	parms = (T2_FNEXT_RSP_PARMS *)response_data;
-	response_data = (char *)&pSMBr->hdr.Protocol +
-		le16_to_cpu(pSMBr->t2.DataOffset);
+	response_data = (char *)&pSMBr->hdr.Protocol + data_off;
 
 	if (psrch_inf->smallBuf)
 		cifs_small_buf_release(psrch_inf->ntwrk_buf_start);
-- 
2.39.5