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 7A70C1F55FA; Sun, 3 Aug 2025 21:19:57 +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=1754255997; cv=none; b=lF1skrBYPl4Aq+dmRMKPoRZCl8iI4VzosJjT9BnWtOU3AnuHtbWrqtAv3/38IgMMCICk7DauXasBQPUBDZtzKFPD+FYgw/xV5w0uou0jZEUBFCZJr5kes0z7ic4PNso83CDaRoT0CleNEsnov4vDa7VdVW66ploxqK4dlfbP9v0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754255997; c=relaxed/simple; bh=lV/u4IEv91CMs8yD9ZwTnQGKcIj8qRopJyPO8M21Cpw=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Md4evZkbEf6fwqQxg88GFqbmQP2yrg+bYGL1onukuJBfS4WXWmrFw5HmaG1L5HEcy8zxVRJPS1bf8MJlcJXgidjbTwkDTfeVpxNYy7kgNL+mSGI8AkTyFSXAbpS+yJNkt3wFFXv64b87vqAZKXFYaRWPTuTrHKwjr7sz+jTDWMA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=t63ZtGsS; 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="t63ZtGsS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ADF33C4CEF0; Sun, 3 Aug 2025 21:19:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1754255997; bh=lV/u4IEv91CMs8yD9ZwTnQGKcIj8qRopJyPO8M21Cpw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t63ZtGsS0CpuMrjy4DEfq8Gt/FtO+vE6DQug2nyagvRgoqGuK12cotPstw2L1sa1y 4iFCPijJe78Uoe/eYwlOLplx/ihR/vrU+HbIZlhUGaiuKJeDDhRPgPIuhB+ABVfgAJ lmQxFymLPMjdd5jF763aq0wYz/G+fe7m06y7QR0GW5dGkIVGz7/HGumJgY75F5He/X MqmNAXoeOB4gudrcWxE3s1dLb6zZcBGmzxQOTBfclecQN6fsadCeLdlh1wpBSePDDa 0JiypisFFfsD3zL/DY9bQRNg1JUia8Ni8UQGIvWFCAzVg+MDcT2INLpK0Ub7MSYsFW eZNNB5Qi+OYsw== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: NeilBrown , Namjae Jeon , Steve French , Sasha Levin , smfrench@gmail.com, linux-cifs@vger.kernel.org Subject: [PATCH AUTOSEL 6.12 08/31] smb/server: avoid deadlock when linking with ReplaceIfExists Date: Sun, 3 Aug 2025 17:19:11 -0400 Message-Id: <20250803211935.3547048-8-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250803211935.3547048-1-sashal@kernel.org> References: <20250803211935.3547048-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.12.41 Content-Transfer-Encoding: 8bit From: NeilBrown [ Upstream commit d5fc1400a34b4ea5e8f2ce296ea12bf8c8421694 ] If smb2_create_link() is called with ReplaceIfExists set and the name does exist then a deadlock will happen. ksmbd_vfs_kern_path_locked() will return with success and the parent directory will be locked. ksmbd_vfs_remove_file() will then remove the file. ksmbd_vfs_link() will then be called while the parent is still locked. It will try to lock the same parent and will deadlock. This patch moves the ksmbd_vfs_kern_path_unlock() call to *before* ksmbd_vfs_link() and then simplifies the code, removing the file_present flag variable. Signed-off-by: NeilBrown Acked-by: Namjae Jeon Signed-off-by: Steve French Signed-off-by: Sasha Levin --- LLM Generated explanations, may be completely bogus: **Backport Status: YES** This commit should be backported to stable kernel trees. Here's my detailed analysis: ## Bug Analysis This commit fixes a critical **deadlock** issue in the ksmbd (SMB server) subsystem. The deadlock occurs in the `smb2_create_link()` function when creating a hard link with the `ReplaceIfExists` flag set and the target file already exists. ### Deadlock Sequence: 1. `ksmbd_vfs_kern_path_locked()` is called and locks the parent directory 2. If the file exists and `ReplaceIfExists` is true, `ksmbd_vfs_remove_file()` is called while the parent is still locked 3. `ksmbd_vfs_link()` is then called, which attempts to lock the same parent directory again 4. **Result: Deadlock** - the function tries to acquire a lock it already holds ### Fix Implementation: The fix reorders the operations by: - Moving the `ksmbd_vfs_kern_path_unlock()` call to execute **before** `ksmbd_vfs_link()` - This ensures the parent directory is unlocked before attempting the link operation - The code is also simplified by removing the `file_present` flag variable ## Backport Justification: 1. **Critical Bug**: This fixes a deadlock that can hang the kernel's SMB server functionality 2. **User Impact**: The deadlock can be triggered by normal SMB operations (creating hard links with replace), affecting file server availability 3. **Small and Contained**: The fix is minimal - just reordering function calls and simplifying logic 4. **No Architectural Changes**: This is a straightforward bug fix with no feature additions 5. **Low Risk**: The change only affects the specific error path in link creation 6. **Similar to Other Fixes**: The kernel has accepted similar deadlock fixes in ksmbd (e.g., commit 864fb5d37163 "ksmbd: fix possible deadlock in smb2_open") ## Code Quality: The fix properly maintains the locking semantics while avoiding the deadlock. The simplified code flow makes the logic clearer and less error-prone. This is exactly the type of bug fix that stable kernels should receive - it fixes a real issue that affects users, has minimal risk of regression, and improves system stability. fs/smb/server/smb2pdu.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index a97a2885730d..ab1ea8fe1c1b 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -6013,7 +6013,6 @@ static int smb2_create_link(struct ksmbd_work *work, { char *link_name = NULL, *target_name = NULL, *pathname = NULL; struct path path, parent_path; - bool file_present = false; int rc; if (buf_len < (u64)sizeof(struct smb2_file_link_info) + @@ -6046,11 +6045,8 @@ static int smb2_create_link(struct ksmbd_work *work, if (rc) { if (rc != -ENOENT) goto out; - } else - file_present = true; - - if (file_info->ReplaceIfExists) { - if (file_present) { + } else { + if (file_info->ReplaceIfExists) { rc = ksmbd_vfs_remove_file(work, &path); if (rc) { rc = -EINVAL; @@ -6058,21 +6054,17 @@ static int smb2_create_link(struct ksmbd_work *work, link_name); goto out; } - } - } else { - if (file_present) { + } else { rc = -EEXIST; ksmbd_debug(SMB, "link already exists\n"); goto out; } + ksmbd_vfs_kern_path_unlock(&parent_path, &path); } - rc = ksmbd_vfs_link(work, target_name, link_name); if (rc) rc = -EINVAL; out: - if (file_present) - ksmbd_vfs_kern_path_unlock(&parent_path, &path); if (!IS_ERR(link_name)) kfree(link_name); -- 2.39.5