From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D5571A682E for ; Fri, 24 Apr 2026 13:04:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777035846; cv=none; b=NROSbuNdq4Zs6EuKm110Ccop3atFt1+gq5VAUAUw/uV2LH6Gnu5NKGasrknz/Iasjl9ARGC0StF+fG6LyBVtFAGSyYtxiczS5lzXlqaascCBkFyBzdAXBD1X+53t+/joPGbvi7jXG4FuAfNJ0G18ntksdNFnAXndr8HZghFLW3M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777035846; c=relaxed/simple; bh=Flr0gq+o36P1bwo6nFPjP/1G5zmHhSlJa+6ivBb8FVM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=noSrrVdAJr3jemeOwLQcGzZZXlx0uLGmWgll9sc7mm7+fjaX+EiY28CJARhUDVdr6kQaojRPMto9opi+xf7+sHJdSzDNaPEoRe8ITzHDhMBxd48fOZoJL/+4DtN0firOVgYv10xXqP+TDP1KXT3icBISHr5bPwslP14uCoBeOB0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jNVcMEBq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jNVcMEBq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6E291C2BCB2; Fri, 24 Apr 2026 13:04:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777035846; bh=Flr0gq+o36P1bwo6nFPjP/1G5zmHhSlJa+6ivBb8FVM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jNVcMEBqvQwRlAIw0wsMdvnbYEirVC6oIYBzwjnje/zjHEennzKz0cQrUgE/aRxvo 5kkUiBLmc2Qgq9ue5hMT1RFX33r6cYfBSxivQsIUplN200mXhK+Yw+A7MnsaquvKxM MiwuUkGbtPaePlISenhbOBsVWmwz8JI7T/clCQflZIMBISze6OfhdiFER5C+a9Cgt3 PlMaVvcw/kT0fIKi42wIslhd/65ru/uFWHm1UgC8PBgvOECiYSy29t90i2RuWmjai7 2oziBgl+VYAai2jCH8oYhUhMbO5VSIJ0BZeJcV6Vaydqi33luALHsyWZsf0Je0o8fD 5Oe1njus4bn4g== From: Sasha Levin To: stable@vger.kernel.org Cc: Michael Bommarito , Namjae Jeon , Steve French , Sasha Levin Subject: [PATCH 6.6.y 3/3] ksmbd: require minimum ACE size in smb_check_perm_dacl() Date: Fri, 24 Apr 2026 09:04:01 -0400 Message-ID: <20260424130401.1917926-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260424130401.1917926-1-sashal@kernel.org> References: <2026042426-growing-dime-ce6e@gregkh> <20260424130401.1917926-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Michael Bommarito [ Upstream commit d07b26f39246a82399661936dd0c853983cfade7 ] Both ACE-walk loops in smb_check_perm_dacl() only guard against an under-sized remaining buffer, not against an ACE whose declared `ace->size` is smaller than the struct it claims to describe: if (offsetof(struct smb_ace, access_req) > aces_size) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size) break; The first check only requires the 4-byte ACE header to be in bounds; it does not require access_req (4 bytes at offset 4) to be readable. An attacker who has set a crafted DACL on a file they own can declare ace->size == 4 with aces_size == 4, pass both checks, and then granted |= le32_to_cpu(ace->access_req); /* upper loop */ compare_sids(&sid, &ace->sid); /* lower loop */ reads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at offset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES * 4 bytes). Tighten both loops to require ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE which is the smallest valid on-wire ACE layout (4-byte header + 4-byte access_req + 8-byte sid base with zero sub-auths). Also reject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES before letting compare_sids() dereference sub_auth[] entries. parse_sec_desc() already enforces an equivalent check (lines 441-448); smb_check_perm_dacl() simply grew weaker validation over time. Reachability: authenticated SMB client with permission to set an ACL on a file. On a subsequent CREATE against that file, the kernel walks the stored DACL via smb_check_perm_dacl() and triggers the OOB read. Not pre-auth, and the OOB read is not reflected to the attacker, but KASAN reports and kernel state corruption are possible. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Assisted-by: Codex:gpt-5-4 Signed-off-by: Michael Bommarito Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Sasha Levin --- fs/smb/server/smbacl.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index 10fdbaef1d37f..77662612b61d1 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1289,10 +1289,13 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = acl_size - sizeof(struct smb_acl); for (i = 0; i < le16_to_cpu(pdacl->num_aces); i++) { - if (offsetof(struct smb_ace, access_req) > aces_size) + if (offsetof(struct smb_ace, sid) + + aces_size < CIFS_SID_BASE_SIZE) break; ace_size = le16_to_cpu(ace->size); - if (ace_size > aces_size) + if (ace_size > aces_size || + ace_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; aces_size -= ace_size; granted |= le32_to_cpu(ace->access_req); @@ -1310,13 +1313,19 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = acl_size - sizeof(struct smb_acl); for (i = 0; i < le16_to_cpu(pdacl->num_aces); i++) { - if (offsetof(struct smb_ace, access_req) > aces_size) + if (offsetof(struct smb_ace, sid) + + aces_size < CIFS_SID_BASE_SIZE) break; ace_size = le16_to_cpu(ace->size); - if (ace_size > aces_size) + if (ace_size > aces_size || + ace_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; aces_size -= ace_size; + if (ace->sid.num_subauth > SID_MAX_SUB_AUTHORITIES) + break; + if (!compare_sids(&sid, &ace->sid) || !compare_sids(&sid_unix_NFS_mode, &ace->sid)) { found = 1; -- 2.53.0