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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-434af653596sm314104f8f.14.2026.01.14.08.51.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Jan 2026 08:51:11 -0800 (PST) Date: Wed, 14 Jan 2026 16:51:09 +0000 From: David Laight To: Al Viro Cc: linux-fsdevel@vger.kernel.org, Linus Torvalds , Christian Brauner , Jan Kara , Mateusz Guzik , Paul Moore , Jens Axboe , audit@vger.kernel.org, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 68/68] sysfs(2): fs_index() argument is _not_ a pathname Message-ID: <20260114165109.60e46e14@pumpkin> In-Reply-To: <20260114143555.GV3634291@ZenIV> References: <20260114043310.3885463-1-viro@zeniv.linux.org.uk> <20260114043310.3885463-69-viro@zeniv.linux.org.uk> <20260114104155.708180fc@pumpkin> <20260114143555.GV3634291@ZenIV> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 14 Jan 2026 14:35:55 +0000 Al Viro wrote: > On Wed, Jan 14, 2026 at 10:41:55AM +0000, David Laight wrote: > > On Wed, 14 Jan 2026 04:33:10 +0000 > > Al Viro wrote: > > > > > ... it's a filesystem type name. > > > > > > Signed-off-by: Al Viro > > > --- > > > fs/filesystems.c | 9 +++------ > > > 1 file changed, 3 insertions(+), 6 deletions(-) > > > > > > diff --git a/fs/filesystems.c b/fs/filesystems.c > > > index 95e5256821a5..0c7d2b7ac26c 100644 > > > --- a/fs/filesystems.c > > > +++ b/fs/filesystems.c > > > @@ -132,24 +132,21 @@ EXPORT_SYMBOL(unregister_filesystem); > > > static int fs_index(const char __user * __name) > > > { > > > struct file_system_type * tmp; > > > - struct filename *name; > > > + char *name __free(kfree) = strndup_user(__name, PATH_MAX); > > > int err, index; > > > > > > - name = getname(__name); > > > - err = PTR_ERR(name); > > > if (IS_ERR(name)) > > > - return err; > > > + return PTR_ERR(name); > > > > Doesn't that end up calling kfree(name) and the check in kfree() doesn't > > seem to exclude error values. > > include/linux/slab.h:523:DEFINE_FREE(kfree, void *, if (!IS_ERR_OR_NULL(_T)) kfree(_T)) > > kfree() the function won't be even called in that case... I wasn't expecting the code to be optimised for the pointer being invalid. I guess one of the defines does a 'dance' so that the pointer can be returned without kfree() being called - and that needs a check in the function itself. (I'm sure I remember something about the compiler optimising at all away.) Perhaps the test could be: if (!statically_true(IS_ERR_OR_NULL(_T)) kfree(_T) adjusting the check in kfree() to ignore -4096..16 not just 0..16. That should reduce code size without slowing down the 'normal' paths and possibly speeding up the error paths. David