[PATCH 1/2] cifs: fix integer overflow in match_server()

[Roman Smirnov]

The echo_interval is not limited in any way during mounting,
which makes it possible to write a large number to it. This can
cause an overflow when multiplying ctx->echo_interval by HZ in
match_server().

Add constraints for echo_interval to smb3_fs_context_parse_param().

Found by Linux Verification Center (linuxtesting.org) with Svace.

Fixes: adfeb3e00e8e1 ("cifs: Make echo interval tunable")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Roman Smirnov <r.smirnov@xxxxxx>
---
 fs/smb/client/fs_context.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index 8c73d4d60d1a..e38521a713a6 100644
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -1377,6 +1377,11 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 		ctx->closetimeo = HZ * result.uint_32;
 		break;
 	case Opt_echo_interval:
+		if (result.uint_32 < SMB_ECHO_INTERVAL_MIN ||
+		    result.uint_32 > SMB_ECHO_INTERVAL_MAX) {
+			cifs_errorf(fc, "echo interval is out of bounds\n");
+			goto cifs_parse_mount_err;
+		}
 		ctx->echo_interval = result.uint_32;
 		break;
 	case Opt_snapshot:
-- 
2.34.1