ksmbd: fix overflow in dacloffset bounds check

stable inclusion
from stable-v6.15-rc1
commit beff0bc
category: bugfix
CVE: CVE-2025-22039

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=beff0bc9d69bc8e733f9bca28e2d3df5b3e10e42

--------------------------------

The dacloffset field was originally typed as int and used in an
unchecked addition, which could overflow and bypass the existing
bounds check in both smb_check_perm_dacl() and smb_inherit_dacl().

This could result in out-of-bounds memory access and a kernel crash
when dereferencing the DACL pointer.

This patch converts dacloffset to unsigned int and uses
check_add_overflow() to validate access to the DACL.

Cc: stable@vger.kernel.org
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
(cherry picked from commit beff0bc)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>

Conflicts:
	fs/smb/server/smbacl.c

Author: nszetei

fs/smb/server/smbacl.c

@@ -1031,16 +1031,21 @@ int smb_inherit_dacl(struct ksmbd_conn *conn,
 	struct dentry *parent = path->dentry->d_parent;
 	struct mnt_idmap *idmap = mnt_idmap(path->mnt);
 	int inherited_flags = 0, flags = 0, i, ace_cnt = 0, nt_size = 0, pdacl_size;
-	int rc = 0, num_aces, dacloffset, pntsd_type, pntsd_size, acl_len, aces_size;
+	int rc = 0, num_aces, pntsd_type, pntsd_size, acl_len, aces_size;
+	unsigned int dacloffset;
+	size_t dacl_struct_end;
 	char *aces_base;
 	bool is_dir = S_ISDIR(d_inode(path->dentry)->i_mode);
 
 	pntsd_size = ksmbd_vfs_get_sd_xattr(conn, idmap,
 					    parent, &parent_pntsd);
 	if (pntsd_size <= 0)
 		return -ENOENT;
+
 	dacloffset = le32_to_cpu(parent_pntsd->dacloffset);
-	if (!dacloffset || (dacloffset + sizeof(struct smb_acl) > pntsd_size)) {
+	if (!dacloffset ||
+	    check_add_overflow(dacloffset, sizeof(struct smb_acl), &dacl_struct_end) ||
+	    dacl_struct_end > (size_t)pntsd_size) {
 		rc = -EINVAL;
 		goto free_parent_pntsd;
 	}
@@ -1243,7 +1248,9 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path,
 	struct smb_ntsd *pntsd = NULL;
 	struct smb_acl *pdacl;
 	struct posix_acl *posix_acls;
-	int rc = 0, pntsd_size, acl_size, aces_size, pdacl_size, dacl_offset;
+	int rc = 0, pntsd_size, acl_size, aces_size, pdacl_size;
+	unsigned int dacl_offset;
+	size_t dacl_struct_end;
 	struct smb_sid sid;
 	int granted = le32_to_cpu(*pdaccess & ~FILE_MAXIMAL_ACCESS_LE);
 	struct smb_ace *ace;
@@ -1262,7 +1269,8 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path,
 
 	dacl_offset = le32_to_cpu(pntsd->dacloffset);
 	if (!dacl_offset ||
-	    (dacl_offset + sizeof(struct smb_acl) > pntsd_size))
+	    check_add_overflow(dacl_offset, sizeof(struct smb_acl), &dacl_struct_end) ||
+	    dacl_struct_end > (size_t)pntsd_size)
 		goto err_out;
 
 	pdacl = (struct smb_acl *)((char *)pntsd + le32_to_cpu(pntsd->dacloffset));