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Wed, 10 Dec 2025 10:02:39 -0800 (PST) Received: from dkarn-thinkpadp16vgen1.punetw6.csb ([2402:e280:3e0d:a45:3861:8b7f:6ae1:6229]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c0c2bfa0845sm128206a12.28.2025.12.10.10.02.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Dec 2025 10:02:38 -0800 (PST) From: Deepakkumar Karn To: Alexander Viro Cc: Christian Brauner , Jan Kara , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Deepakkumar Karn Subject: [PATCH] fs/buffer: add alert in try_to_free_buffers() for folios without buffers Date: Wed, 10 Dec 2025 23:32:28 +0530 Message-ID: <20251210180228.211655-1-dkarn@redhat.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" try_to_free_buffers() can be called on folios with no buffers attached when filemap_release_folio() is invoked on a folio belonging to a mapping with AS_RELEASE_ALWAYS set but no release_folio operation defined. In such cases, folio_needs_release() returns true because of the AS_RELEASE_ALWAYS flag, but the folio has no private buffer data. This causes try_to_free_buffers() to call drop_buffers() on a folio with no buffers, leading to a null pointer dereference. Adding a check in try_to_free_buffers() to return early if the folio has no buffers attached, with WARN_ON_ONCE() to alert about the misconfiguration. This provides defensive hardening. Signed-off-by: Deepakkumar Karn --- fs/buffer.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/buffer.c b/fs/buffer.c index 838c0c571022..b229baa77055 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -2948,6 +2948,10 @@ bool try_to_free_buffers(struct folio *folio) if (folio_test_writeback(folio)) return false; =20 + /* Misconfigured folio check */ + if (WARN_ON_ONCE(!folio_buffers(folio))) + return false; + if (mapping =3D=3D NULL) { /* can this still happen? */ ret =3D drop_buffers(folio, &buffers_to_free); goto out; --=20 2.52.0