From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 65408288BA for ; Sun, 5 Jul 2026 19:06:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783278394; cv=none; b=AQMBt8JKErzRv7X5m7HwX/Bj5INVLJvJe+7eXUAjU+ITK8SgilgY4NCbFhbTln0kpnHQQ+miCEYwEPXYCLJ6XoBAp9C0lzec5i8Upn5zhYZJRAIYu3wJW2JElPCVqjMBnhooAR8HZQHJqH5lNbiYIsUqHM4GnbW/3L2/yN4Ixjc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783278394; c=relaxed/simple; bh=PE8rub0DLKeH7k0oe8Ru1CelA8MsqIbMl+CmZtq/EXY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K56nznnLJ/AxkpY19C0CQUn3nOXt5BuqrpBP/QgxBrpQkl2f2ZBrElcOp1ZLJggfUJchJ0RS+4SpZhQmWA4wIux5ACqtr5eAihFtt8DmMWxD8xlNnIjUTm0mPFrtJ43yBVSGM7CgMLLokOBYlyvpAHJYWAU1OCoce7pSLCJGI8I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bGYbtzRz; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bGYbtzRz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6AA2D1F000E9; Sun, 5 Jul 2026 19:06:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783278393; bh=8kyDptHl87sbVh5YYfW3rA9YgOQIlcECiARsy3Vj+/s=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bGYbtzRzbYj072una64p8/WXQDluH3lqmT6xVqhHUmg4ENwbtEkzcbtyB6E0yhkmy kjV82NptXMwaC8FhyR9QOA7AetAnafvlGNxiQA6kN1jjs7lNeN27B4Gd2cEgXcza3N elTlmF/6YdV87OyMXUwW6f4szqpE3InrI36/f+LU3IXCNWE0OimJCCT/7YoSMOvzBQ Zz3bCOChaFT6LvMRfinJdJ0NUsAQAG6kDZn3BsFvbr4LcyUUa6fptruqckfNm2Zt7E Q3LluFhckTZowyVwNdoqK6nQg05bq1OerlIfhXVBwtOIJC9F2vAZXlr5/s3Iz06DKT kHvuOaNI554/A== From: Sasha Levin To: stable@vger.kernel.org Cc: Hem Parekh , Namjae Jeon , Steve French , Sasha Levin Subject: [PATCH 5.15.y] ksmbd: fix out-of-bounds read in smb_check_perm_dacl() Date: Sun, 5 Jul 2026 15:06:30 -0400 Message-ID: <20260705190630.1988235-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026070254-saddling-prankish-2dc9@gregkh> References: <2026070254-saddling-prankish-2dc9@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hem Parekh [ Upstream commit 1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b ] The permission-check ACE walk in smb_check_perm_dacl() validates the ACE header size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it never checks that ace->size is actually large enough to contain num_subauth sub-authorities before compare_sids() dereferences them. CIFS_SID_BASE_SIZE covers the SID header up to but excluding the sub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header, so the existing guards only guarantee the 8-byte SID base, i.e. zero sub-authorities. compare_sids() then reads ace->sid.sub_auth[i] for i < min(local_sid->num_subauth, ace->sid.num_subauth). The local comparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid() result) always have at least one sub-authority, and an attacker controls the ACE revision and authority bytes (which lie within the in-bounds SID base), so they can match one of those SIDs and force the sub_auth read. A crafted ACE with size == 16 and num_subauth >= 1 placed at the tail of the security descriptor therefore causes a heap out-of-bounds read of up to SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd allocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr() into a buffer sized exactly to the on-disk data (kzalloc(sd_size) in ndr_decode_v4_ntacl()), so the read lands past the allocation. The malformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL is not normalised before being written to the security.NTACL xattr) and the read fires on a subsequent SMB2_CREATE access check, making this reachable by an authenticated client on a share that uses ACL xattrs. Add the missing num_subauth-versus-ace_size check, mirroring the identical guards already present in the sibling parsers parse_dacl() and smb_inherit_dacl(). Fixes: d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") Cc: stable@vger.kernel.org Signed-off-by: Hem Parekh Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Sasha Levin --- fs/ksmbd/smbacl.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/ksmbd/smbacl.c b/fs/ksmbd/smbacl.c index 5e21424aa97adc..cf5361b63c7dbc 100644 --- a/fs/ksmbd/smbacl.c +++ b/fs/ksmbd/smbacl.c @@ -1299,7 +1299,9 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, break; aces_size -= ace_size; - if (ace->sid.num_subauth > SID_MAX_SUB_AUTHORITIES) + if (ace->sid.num_subauth > SID_MAX_SUB_AUTHORITIES || + ace_size < offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE + + sizeof(__le32) * ace->sid.num_subauth) break; if (!compare_sids(&sid, &ace->sid) || -- 2.53.0