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 D80BC3537DF; Fri, 24 Apr 2026 13:43:50 +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=1777038230; cv=none; b=faPE8x2l9N9lYgw9zSY1i8AlVsyXMm+FsLQ2PAsiGcCT0ZULpxXJmmjn3UVsF+L18kd1cSGdarCpTkuUzoG9HpL0lIkdQWuPLY3e3Yx/tGuvtNNPwlgt6ZfOohsGVsUWKuDmCbzSHO6/HGfSjwiQ77n9UvxjOZQhOuwuq+yVu+A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777038230; c=relaxed/simple; bh=ObikQVB//IjHqORbcXSZBzbrHibOeNbOgcg9e3ltelw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=gCGx+WQ/GEdBYtXwO5x8wLeSbc4GoPLE+kg0vPOXLUIGcfg0vmNdZYT/BXgm9rF+LGirVEXvNWICG2bOZVJeZO7RmRJJaeH2Q6QnkQS4BMGkj4izH4Amf5cWeci3dCoyVtRPVeySCkrWywAlvBZyj7rLLqSy2ty6pTY2oOnHds4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Z+H61YJg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Z+H61YJg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6649BC19425; Fri, 24 Apr 2026 13:43:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1777038230; bh=ObikQVB//IjHqORbcXSZBzbrHibOeNbOgcg9e3ltelw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z+H61YJgddGUFMI/RVZj4rqkpd3YUQSwtpe3rvCNLqTWYjv8oCdW6ZNCuC0dqFBMX K9l0RcZRHFhtlQlBl/50uKTpMuEryP0W/y/kOVJmAT+ehU55dR4t/41eXw2H+zce2L mNP0rXK2tVJaW/Ty+yDBDUVlKVONP4dPzhVu5PHg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Michael Bommarito , Namjae Jeon , Steve French Subject: [PATCH 6.12 19/35] ksmbd: require minimum ACE size in smb_check_perm_dacl() Date: Fri, 24 Apr 2026 15:31:26 +0200 Message-ID: <20260424132415.724156906@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260424132411.427029259@linuxfoundation.org> References: <20260424132411.427029259@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael Bommarito commit d07b26f39246a82399661936dd0c853983cfade7 upstream. 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: Greg Kroah-Hartman --- fs/smb/server/smbacl.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1342,10 +1342,13 @@ int smb_check_perm_dacl(struct ksmbd_con 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); @@ -1363,13 +1366,19 @@ int smb_check_perm_dacl(struct ksmbd_con 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;