[PATCH v4 07/10] smb: client: fix missing iov bounds check in parse_posix_sids()

[Frank Sorenson <sorenson@redhat.com>]

In parse_posix_sids(), sidsbuf_end is calculated using the server-supplied
out_len without being validated against the actual length of the received
iov (iov_len).

If a server provides an inflated out_len, sidsbuf_end will point past the
end of the iov. This defeats the bounds guards in posix_info_sid_size(),
allowing out-of-bounds reads into adjacent kernel memory.

Fix this by rejecting responses where the calculated sidsbuf_end would
exceed the received iov boundaries or cause pointer wraparound.

Fixes: a90f37e3d7ac ("smb: client: parse owner/group when creating reparse points")
Cc: stable@vger.kernel.org
Signed-off-by: Frank Sorenson <sorenson@redhat.com>
---
 fs/smb/client/smb2inode.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/smb/client/smb2inode.c b/fs/smb/client/smb2inode.c
index 96063e355186..13fe8e3b48f3 100644
--- a/fs/smb/client/smb2inode.c
+++ b/fs/smb/client/smb2inode.c
@@ -77,6 +77,17 @@ static int parse_posix_sids(struct cifs_open_info_data *data,
 
 	sidsbuf = (u8 *)qi + le16_to_cpu(qi->OutputBufferOffset) + qi_len;
 	sidsbuf_end = sidsbuf + out_len - qi_len;
+	if (sidsbuf_end < sidsbuf) {
+		cifs_dbg(VFS, "%s: server-supplied out_len %u caused pointer wraparound\n",
+			 __func__, out_len);
+		return -EINVAL;
+	}
+	if (sidsbuf_end > (u8 *)rsp_iov->iov_base + rsp_iov->iov_len) {
+		cifs_dbg(VFS, "%s: server-supplied out_len %u overruns iov by %td bytes\n",
+			 __func__, out_len,
+			 sidsbuf_end - ((u8 *)rsp_iov->iov_base + rsp_iov->iov_len));
+		return -EINVAL;
+	}
 
 	owner_len = posix_info_sid_size(sidsbuf, sidsbuf_end);
 	if (owner_len == -1)
-- 
2.55.0