FAILED: patch "[PATCH] ksmbd: restore DACL size on check_add_overflow() to avoid" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x bbf0a8e931204ecdab494a88d43b0a24a04285c5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072936-idealist-delicate-86ff@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From bbf0a8e931204ecdab494a88d43b0a24a04285c5 Mon Sep 17 00:00:00 2001
From: Wentao Guan <[email protected]>
Date: Fri, 3 Jul 2026 11:22:09 +0900
Subject: [PATCH] ksmbd: restore DACL size on check_add_overflow() to avoid
malformed ACL

check_add_overflow() unconditionally writes the truncated sum into *d even on overflow, per its contract in include/linux/overflow.h. The four check_add_overflow() guards in set_posix_acl_entries_dacl() and set_ntacl_dacl() break out of the ACE-building loops on overflow, but the truncated *size is then consumed downstream at the end of set_ntacl_dacl():

    pndacl->size = cpu_to_le16(le16_to_cpu(pndacl->size) + size);

This produces an on-wire NT ACL whose pndacl->size under-reports the bytes actually written by the preceding fill_ace_for_sid()/memcpy() calls, yielding a malformed ACL that can trigger out-of-bounds reads when re-parsed by clients or ksmbd itself.

Restore *size to its pre-addition value on each overflow branch (via *size -= ace_sz / size -= nt_ace_size) so that after the break, *size once again holds the cumulative size of the successfully-written ACEs. The committed ACL is then truncated-but-self-consistent rather than malformed.

The ksmbd DACL builders are the only check_add_overflow() sites found where an overflow path breaks out of a loop and the destination value is consumed afterward. The other nearby break-style cases either return -EINVAL on overflow (transport_ipc.c) or break without consuming the overflowed destination value afterward (buildid.c).

index d28289188e44..f285b4f24a5b 100644
@@ -663,6 +663,7 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap,
 		ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, flags,
 				pace->e_perm, 0777);
 		if (check_add_overflow(*size, ace_sz, size)) {
+			*size -= ace_sz;
 			kfree(sid);
 			break;
 		}

@@ -677,6 +678,7 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap,
 			ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED,
 					0x03, pace->e_perm, 0777);
 			if (check_add_overflow(*size, ace_sz, size)) {
+				*size -= ace_sz;
 				kfree(sid);
 				break;
 			}

@@ -722,6 +724,7 @@ static void set_posix_acl_entries_dacl(struct mnt_idmap *idmap,
 		ace_sz = fill_ace_for_sid(ntace, sid, ACCESS_ALLOWED, 0x0b,
 				pace->e_perm, 0777);
 		if (check_add_overflow(*size, ace_sz, size)) {
+			*size -= ace_sz;
 			kfree(sid);
 			break;
 		}

@@ -765,8 +768,10 @@ static void set_ntacl_dacl(struct mnt_idmap *idmap,
 				goto next_ace;
 
 			memcpy((char *)pndace + size, ntace, nt_ace_size);
-			if (check_add_overflow(size, nt_ace_size, &size))
+			if (check_add_overflow(size, nt_ace_size, &size)) {
+				size -= nt_ace_size;
 				break;
+			}
 			num_aces++;
 
 next_ace: