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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49982165351sm849785e9.10.2026.08.12.12.33.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 12 Aug 2026 12:33:56 -0700 (PDT) From: David Laight To: Chuck Lever , Jeff Layton , NeilBrown , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Banks Cc: David Laight , Olga Kornievskaia , Dai Ngo , Tom Talpey , Andrew Morton , Linus Torvalds Subject: [PATCH net-next] fs: nfsd: Fix buffer overflow in write_pool_threads() Date: Wed, 12 Aug 2026 20:33:49 +0100 Message-Id: <20260812193349.13347-1-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit write_pool_threads() writes the number of threads in each pool into a caller-supplied 'almost PAGE_SIZE' buffer. If there are enough pools to overflow the buffer the code continues writing beynd its end. Fix the overflow check so that it actually works. Fixes: eed2965af1bae "knfsd: allow admin to set nthreads per node" Signed-off-by: David Laight --- I'm pretty sure this is 'root only' code. So you'd have to try very hard to actually get the overflow. fs/nfsd/nfsctl.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c index 39e7012a60d8..b74048aa2402 100644 --- a/fs/nfsd/nfsctl.c +++ b/fs/nfsd/nfsctl.c @@ -483,8 +483,7 @@ static ssize_t write_pool_threads(struct file *file, char *buf, size_t size) * file, sorry. Report zero threads. */ mutex_unlock(&nfsd_mutex); - strcpy(buf, "0\n"); - return strlen(buf); + return strscpy(buf, "0\n", SIMPLE_TRANSACTION_LIMIT); } nthreads = kzalloc_objs(int, npools); @@ -523,13 +522,14 @@ static ssize_t write_pool_threads(struct file *file, char *buf, size_t size) mesg = buf; size = SIMPLE_TRANSACTION_LIMIT; - for (i = 0; i < npools && size > 0; i++) { - snprintf(mesg, size, "%d%c", nthreads[i], (i == npools-1 ? '\n' : ' ')); - len = strlen(mesg); + for (i = 0; i < npools; i++) { + len = scnprintf(mesg, size, "%d ", nthreads[i]); size -= len; mesg += len; } rv = mesg - buf; + if (rv != SIMPLE_TRANSACTION_LIMIT - 1) + msg[-1] = '\n'; out_free: kfree(nthreads); mutex_unlock(&nfsd_mutex); -- 2.39.5