cifs: Fix integer overflow while processing acdirmax mount option

JIRA: https://issues.redhat.com/browse/RHEL-87940
CVE: CVE-2025-21963

commit 5b29891
Author: Murad Masimov <[email protected]>
Date:   Tue Mar 11 17:22:04 2025 +0300

    cifs: Fix integer overflow while processing acdirmax mount option
    
    User-provided mount parameter acdirmax of type u32 is intended to have
    an upper limit, but before it is validated, the value is converted from
    seconds to jiffies which can lead to an integer overflow.
    
    Found by Linux Verification Center (linuxtesting.org) with SVACE.
    
    Fixes: 4c9f948 ("cifs: Add new mount parameter "acdirmax" to allow caching directory metadata")
    Signed-off-by: Murad Masimov <[email protected]>
    Signed-off-by: Steve French <[email protected]>

Signed-off-by: Paulo Alcantara <[email protected]>

Author: pcacjr

fs/smb/client/fs_context.c

@@ -1366,11 +1366,11 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 		ctx->acregmax = HZ * result.uint_32;
 		break;
 	case Opt_acdirmax:
-		ctx->acdirmax = HZ * result.uint_32;
-		if (ctx->acdirmax > CIFS_MAX_ACTIMEO) {
+		if (result.uint_32 > CIFS_MAX_ACTIMEO / HZ) {
 			cifs_errorf(fc, "acdirmax too large\n");
 			goto cifs_parse_mount_err;
 		}
+		ctx->acdirmax = HZ * result.uint_32;
 		break;
 	case Opt_actimeo:
 		if (HZ * result.uint_32 > CIFS_MAX_ACTIMEO) {