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 2B54231716A for ; Sat, 5 Sep 2026 01:50:02 +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=1788573003; cv=none; b=UKkIYLVPlKr5LwzoUoya/jsKN6/q+/dMeOisTSNHZunckBvOaj53QbaYB4zBhLGv4ov8RVfGsb8NsT6JstwBs1F7Zk0E4+Vvc3BLGzaS+13X7Kmqz12/X0M1Bm/2NVjLq7iecaZXnrfuHCs0Go7+5X3OjhsP4C8S2AafCNqWdjg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788573003; c=relaxed/simple; bh=TxWJnS9fWcYd/CEaJ6J/6OLzkJQD+5uttjsAzBfj3N4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eNOhzE+pLtiMSHx6Lnx6lMe6SaaEufRF0o1aNUqI56f0t1WKPYT8QJwr+GXe0x1VaoCyvWJgPl7sDFu7k3K2Xei7bkx/YGgVqcUw2BTFbP0vZBoKiLsIdhU3xQ1RmX/9P+3wuWb2AXZ+8xjlnI6vUhXPuKxQ1zguFmllo0H/K7I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n4S2xc97; 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="n4S2xc97" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 449BC1F00A3F; Sat, 5 Sep 2026 01:50:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788573001; bh=axqPrUR/RwcwQtV+k9wGZL3/cmX3Z3nfy/OnGemvy1A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=n4S2xc97Xikc7LQIg/hcwcvGTFf9poPNSqwhHywFtquDUbpv9naB9Wb/UapSvxxga iYISG3MGx07Ox6LNWZVta/JufUHeE+T8MQZPgv9WDzUcUzxnW7RgiYNkBeg0iub/jJ ECdoTFjdmWErnUBO6LD+O+hlBzLuWJXGkbxU3nFucbBZYXD5qDlXNxITW+bSY2zo6N RJae0VFIEje3bK0+K9laeZbUcJvpRWnwxxnqgEyubMyXkG9+25nB7hk0DbRjjOR4sm ML29MPZC34sOdcQqe0YHbNljdsov6YARTRl9lMqFcQy9DYhHHvZnu+/GoBdk6f8Rt9 t021N526l/PVg== From: Sasha Levin To: stable@vger.kernel.org Cc: Chuck Lever , Chris Mason , Jeff Layton , Sasha Levin Subject: [PATCH 5.10.y 2/2] NFSD: check truncate permission under inode lock Date: Fri, 4 Sep 2026 21:49:58 -0400 Message-ID: <20260905014958.1806867-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260905014958.1806867-1-sashal@kernel.org> References: <2026090340-darkness-disposal-745f@gregkh> <20260905014958.1806867-1-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: Chuck Lever [ Upstream commit b778e0e0a16759f22a70579c3cf8d254a40d4a7f ] nfsd_setattr() checks whether a size update needs NFSD_MAY_TRUNC before it takes inode_lock(). The comparison uses the file size sampled by that unlocked read, but the actual ATTR_SIZE update is applied later under inode_lock() by notify_change(). This leaves a TOCTOU window for append-only files. If a client sends a SETATTR that does not shrink the file at the time of the unlocked sample, a concurrent append can extend the file before nfsd_setattr() takes inode_lock(). notify_change() then applies a real truncation without the NFSD_MAY_TRUNC check that rejects IS_APPEND(inode). The VFS truncate syscall paths perform their own append-only checks before calling notify_change(), so NFSD must make this decision against the locked size it is about to change. Split the write-count acquisition from the truncation permission check. Keep get_write_access() before the locked setattr work, then recheck whether the requested size is below i_size_read(inode) after inode_lock() has been acquired and before notify_change(ATTR_SIZE). This also avoids the plain unlocked inode->i_size load. Fixes: 783112f7401f ("nfsd: special case truncates some more") Cc: stable@vger.kernel.org Assisted-by: kres:claude-opus-4-7 Reported-by: Chris Mason Signed-off-by: Jeff Layton Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-6-f27e8eb4d974@kernel.org Signed-off-by: Chuck Lever Signed-off-by: Sasha Levin --- fs/nfsd/vfs.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 064074dbb64b5..429521b0d194c 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -390,21 +390,22 @@ nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap) } static __be32 -nfsd_get_write_access(struct svc_rqst *rqstp, struct svc_fh *fhp, - struct iattr *iap) +nfsd_may_truncate(struct svc_rqst *rqstp, struct svc_fh *fhp, + struct iattr *iap) { struct inode *inode = d_inode(fhp->fh_dentry); - if (iap->ia_size < inode->i_size) { - __be32 err; + if (iap->ia_size >= i_size_read(inode)) + return nfs_ok; - err = nfsd_permission(&rqstp->rq_cred, - fhp->fh_export, fhp->fh_dentry, - NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE); - if (err) - return err; - } - return nfserrno(get_write_access(inode)); + return nfsd_permission(&rqstp->rq_cred, fhp->fh_export, fhp->fh_dentry, + NFSD_MAY_TRUNC | NFSD_MAY_OWNER_OVERRIDE); +} + +static __be32 +nfsd_get_write_access(struct svc_fh *fhp) +{ + return nfserrno(get_write_access(d_inode(fhp->fh_dentry))); } static int __nfsd_setattr(struct dentry *dentry, struct iattr *iap) @@ -531,12 +532,17 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, * setattr call. */ if (size_change) { - err = nfsd_get_write_access(rqstp, fhp, iap); + err = nfsd_get_write_access(fhp); if (err) return err; } inode_lock(inode); + if (size_change) { + err = nfsd_may_truncate(rqstp, fhp, iap); + if (err) + goto out_unlock; + } err = fh_fill_pre_attrs(fhp); if (err) goto out_unlock; -- 2.53.0