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Fri, 23 May 2025 11:51:41 -0700 (PDT) Received: from localhost ([196.207.164.177]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-447f78b0acasm146711125e9.31.2025.05.23.11.51.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 May 2025 11:51:40 -0700 (PDT) Date: Fri, 23 May 2025 21:51:36 +0300 From: Dan Carpenter To: Joanne Koong Cc: linux-fsdevel@vger.kernel.org Subject: Re: [bug report] fuse: support copying large folios Message-ID: References: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, May 23, 2025 at 10:32:29AM -0700, Joanne Koong wrote: > On Fri, May 23, 2025 at 8:59 AM Dan Carpenter wrote: > > > > Hello Joanne Koong, > > > > This is a semi-automatic email about new static checker warnings. > > > > Commit f008a4390bde ("fuse: support copying large folios") from May > > 12, 2025, leads to the following Smatch complaint: > > > > fs/fuse/dev.c:1103 fuse_copy_folio() > > warn: variable dereferenced before check 'folio' (see line 1101) > > > > fs/fuse/dev.c > > 1100 struct folio *folio = *foliop; > > 1101 size_t size = folio_size(folio); > > ^^^^^ > > The patch adds an unchecked dereference > > > > 1102 > > 1103 if (folio && zeroing && count < size) > > ^^^^^ > > and it also adds this check for NULL which is too late. > > > > 1104 folio_zero_range(folio, 0, size); > > 1105 > > Thanks for flagging. I looked through where we call fuse_copy_folio() > and we'll never run into the case where folio is null, so all the "if > folio" branches inside there can probably be cleaned up with a WARN_ON > check. > > I'll submit a patch that fixes this commit and a separate patch that > cleans up the if folio check. Another idea is to just crash when people pass a NULL pointer. The stack traces from NULL dereference bugs are normally easy to debug unless they're caused by a race condition or memory corruption. regards, dan carpenter