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 C48F39478; Thu, 2 Oct 2025 15:31:06 +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=1759419066; cv=none; b=Rt0VujNga2ulViu3Va09buCrFc9TBUNIAFPPLZz4y0lO1eIUT6RjyRckw1xUfBEOGLk32pGapUv+cptrrkYLYM8LN/OK5pC6jlmTtu8a8yEpYQOIYTiispC1LV45Dqxwe45BO/afo1NiZCrGIP9ceNnMbzdnUnDmN7GMbzrotpM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759419066; c=relaxed/simple; bh=yAwudebwORFowbq4nAr02Ar/6fOt5VjqBk71MiEGQiw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=TdFvLdT2wkRpKkHBAj/ljrUDrRaJcDbpiQY9JNLI9vUpLahCNySRPLbYLD2JtqzKVQZguL0vSaG4AaIMOWcfRj5epR2A9rtt9jhY81fkaxH++3bH3qtStPqjSM6D2UNgI51o2zZ2ECLmthWjiVnq5mNrBiDWlbkfJGI9X/jDUuo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lLL6/Z64; 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="lLL6/Z64" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 70214C4CEF9; Thu, 2 Oct 2025 15:31:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759419066; bh=yAwudebwORFowbq4nAr02Ar/6fOt5VjqBk71MiEGQiw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lLL6/Z64IJo7TbgAqtlJ00qKIOwiYuGqT2YcJn7yqoerkFaKbQFPmdfGIqejgzMGU U0pZC9s3bMocna3OtMKNmDtC2id6rJdMFrW4H9a7i/DIRN+m4LBRX2tp451VgwCnIQ 4H6iTxDHKXXpXBUcNIOOyKcWNDNXdlQHBgkkgh6nNCBcRq21uNSxlQDoIMVaHzDOBb puZP4zO6AYKAmN/mftroT94u7GmltauewCKnk2XbMal5PWkegJHQhaLZHfHyjjqVG8 tOn2zzkkeV5qyg4ee/Bu8RHhjT4D8s4Hc2X64NZM0u4+VURCGe2ZHziL6R/V7+6Rxf o4dL+8iY3A0Hw== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Stefan Metzmacher , Steve French , Tom Talpey , Long Li , linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, Namjae Jeon , Steve French , Sasha Levin Subject: [PATCH AUTOSEL 6.17] smb: client: limit the range of info->receive_credit_target Date: Thu, 2 Oct 2025 11:30:16 -0400 Message-ID: <20251002153025.2209281-29-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251002153025.2209281-1-sashal@kernel.org> References: <20251002153025.2209281-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.17 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Stefan Metzmacher [ Upstream commit 9219f8cac296769324bbe8a28c289586114244c4 ] This simplifies further changes... Cc: Steve French Cc: Tom Talpey Cc: Long Li Cc: linux-cifs@vger.kernel.org Cc: samba-technical@lists.samba.org Acked-by: Namjae Jeon Signed-off-by: Stefan Metzmacher Signed-off-by: Steve French Signed-off-by: Sasha Levin --- LLM Generated explanations, may be completely bogus: ## Backport Determination: **YES** Based on my comprehensive analysis of this commit and the surrounding SMBDirect subsystem, this commit **should be backported** to stable kernel trees. ### Detailed Analysis #### **1. Nature of the Fix** This commit addresses a **resource exhaustion vulnerability** in the SMBDirect client code. The vulnerability occurs because `receive_credit_target` is set directly from untrusted network data without bounds checking: **Vulnerable code locations (fs/smb/client/smbdirect.c):** - Line 350: `info->receive_credit_target = le16_to_cpu(packet->credits_requested);` - Line 522: `info->receive_credit_target = le16_to_cpu(data_transfer->credits_requested);` #### **2. Security Impact** **Exploit Scenario:** A malicious SMB server can send a `credits_requested` value of up to 65535 (max u16 value). This unbounded value is then used in the credit posting loop (lines 413-430): ```c if (info->receive_credit_target > atomic_read(&info->receive_credits)) { while (true) { response = get_receive_buffer(info); if (!response) break; rc = smbd_post_recv(info, response); ... } } ``` **Consequences:** - **Memory exhaustion**: Attempting to allocate 65535 receive buffers could exhaust kernel memory - **Hardware limit violations**: RDMA hardware has limits (max_cqe, max_qp_wr) that could be exceeded, causing failures - **Denial of service**: System instability or connection failures - **Type mismatch**: Using `int` instead of `u16` for a protocol field can cause subtle bugs #### **3. The Fix** The commit implements three protections: 1. **Upper bound check**: `min_t(u16, info->receive_credit_target, sp->recv_credit_max)` - Limits to `recv_credit_max` (default 255, validated against hardware limits at line 1578-1584) 2. **Lower bound check**: `max_t(u16, info->receive_credit_target, 1)` - Prevents zero or negative values that could break protocol logic 3. **Type correction**: Changes `int receive_credit_target` to `u16 receive_credit_target` - Matches the wire protocol specification (le16) - Prevents sign-related bugs #### **4. Part of Comprehensive Security Hardening** This commit is one of **160+ commits** by Stefan Metzmacher (Samba team) hardening the SMBDirect code. Related security fixes include: - `f57e53ea25236`: "let recv_done verify data_offset, data_length and remaining_data_length" (with `Fixes: f198186aa9bb` tag) - Multiple memory leak fixes in error paths - Improved synchronization and error handling The commit message mentions this is part of a larger effort: "This simplifies further changes..." #### **5. Backport Suitability** ✅ **Fixes important bug**: Resource exhaustion vulnerability ✅ **Small and contained**: Only 9 lines changed across 2 files ✅ **No architectural changes**: Simple bounds checking addition ✅ **Minimal regression risk**: Defensive check that only restricts invalid values ✅ **No dependencies**: Standalone fix, doesn't require other commits ✅ **Subsystem isolation**: Confined to SMBDirect client code ✅ **Already being backported**: Found evidence in linux tree with "Signed-off-by: Sasha Levin " #### **6. Risk Assessment** **Low Risk:** - The changes only add validation to untrusted input - Well-behaved servers will not be affected (they shouldn't request more than the negotiated maximum anyway) - The bounds are based on validated local configuration and hardware capabilities - Type change from `int` to `u16` is safe (values are always from `le16_to_cpu()`) **No identified follow-up fixes or reverts** in the git history. ### Conclusion This is a **security hardening fix** that prevents resource exhaustion attacks from malicious SMB servers. It follows stable kernel rules perfectly: it's an important bugfix with minimal risk and no architectural changes. The fix is part of a comprehensive security review of the SMBDirect subsystem by experienced Samba developers. **Recommendation: Backport to all applicable stable trees supporting SMBDirect (Linux 4.11+)** fs/smb/client/smbdirect.c | 7 ++++++- fs/smb/client/smbdirect.h | 2 +- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c index c9375dc11f634..3fc5d2cebea5d 100644 --- a/fs/smb/client/smbdirect.c +++ b/fs/smb/client/smbdirect.c @@ -348,6 +348,7 @@ static bool process_negotiation_response( return false; } info->receive_credit_target = le16_to_cpu(packet->credits_requested); + info->receive_credit_target = min_t(u16, info->receive_credit_target, sp->recv_credit_max); if (packet->credits_granted == 0) { log_rdma_event(ERR, "error: credits_granted==0\n"); @@ -456,7 +457,7 @@ static void recv_done(struct ib_cq *cq, struct ib_wc *wc) struct smbdirect_socket_parameters *sp = &sc->parameters; struct smbd_connection *info = container_of(sc, struct smbd_connection, socket); - int old_recv_credit_target; + u16 old_recv_credit_target; u32 data_offset = 0; u32 data_length = 0; u32 remaining_data_length = 0; @@ -522,6 +523,10 @@ static void recv_done(struct ib_cq *cq, struct ib_wc *wc) old_recv_credit_target = info->receive_credit_target; info->receive_credit_target = le16_to_cpu(data_transfer->credits_requested); + info->receive_credit_target = + min_t(u16, info->receive_credit_target, sp->recv_credit_max); + info->receive_credit_target = + max_t(u16, info->receive_credit_target, 1); if (le16_to_cpu(data_transfer->credits_granted)) { atomic_add(le16_to_cpu(data_transfer->credits_granted), &info->send_credits); diff --git a/fs/smb/client/smbdirect.h b/fs/smb/client/smbdirect.h index e45aa9ddd71da..d0f734afd4fb1 100644 --- a/fs/smb/client/smbdirect.h +++ b/fs/smb/client/smbdirect.h @@ -63,7 +63,7 @@ struct smbd_connection { int protocol; atomic_t send_credits; atomic_t receive_credits; - int receive_credit_target; + u16 receive_credit_target; /* Memory registrations */ /* Maximum number of RDMA read/write outstanding on this connection */ -- 2.51.0