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Tue, 19 May 2026 07:29:43 -0700 (PDT) Received: from localhost ([2a00:79e0:288a:8:c208:c046:d3db:6b00]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48febe6faeasm108628185e9.26.2026.05.19.07.29.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 07:29:41 -0700 (PDT) From: Jann Horn Date: Tue, 19 May 2026 16:29:38 +0200 Subject: [PATCH v2] fuse: reject fuse_notify() pagecache ops on directories 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="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260519-fuse-dir-pagecache-v2-1-5428fa48e175@google.com> X-B4-Tracking: v=1; b=H4sIANFzDGoC/32NQQrDIBRErxL+uhY1UZKueo+ShejXfGhj0FZag nevzQHKrN7AvNkhYyLMcOl2SFgoU1wbyFMHdjFrQEauMUguNVdiYv6VkTlKbDMBrbELsn6URg1 i0KPU0IZbQk/vQ3qbGy+UnzF9jo8ifu1fXRGsxXPNrVZTz901xBjueLbxAXOt9QurxG9ntQAAA A== X-Change-ID: 20260519-fuse-dir-pagecache-382a54146826 To: Miklos Szeredi Cc: Alexander Viro , Christian Brauner , Jan Kara , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Jann Horn X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1779200979; l=1836; i=jannh@google.com; s=20240730; h=from:subject:message-id; bh=aY8s/riUR8NbcTdsHB4cfFhuuDro+tneP/kG5QuD+PA=; b=1buKvnGP3P5SX8ycYvMxAc4AImC7lHVMZf1DFKNbo8dj6Y1CfP4DCb2dufCQGnMBD01yIA9Cl dQDEyzFgY0FAjBje5ihyZnJzNAi2VXN3Ro9I52ngmP3nqpcFwQkPDRo X-Developer-Key: i=jannh@google.com; a=ed25519; pk=AljNtGOzXeF6khBXDJVVvwSEkVDGnnZZYqfWhP1V+C8= The operations FUSE_NOTIFY_STORE and FUSE_NOTIFY_RETRIEVE allow the FUSE daemon to actively write/read pagecache contents. For directories with FOPEN_CACHE_DIR, the pagecache is used as kernel-internal cache storage, and userspace is not supposed to have direct access to this cache - in particular, fuse_parse_cache() will hit WARN_ON() if the cache contains bogus data. Reject FUSE_NOTIFY_STORE and FUSE_NOTIFY_RETRIEVE on anything other than regular files with -EINVAL. Fixes: 5d7bc7e8680c ("fuse: allow using readdir cache") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Acked-by: Miklos Szeredi --- Changes in v2: - reject anything other than regular files (Miklos) - Link to v1: https://lore.kernel.org/r/20260519-fuse-dir-pagecache-v1-1-1f= 060c65930d@google.com --- fs/fuse/dev.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 5dda7080f4a9..f07c97358b36 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -1793,6 +1793,10 @@ static int fuse_notify_store(struct fuse_conn *fc, u= nsigned int size, inode =3D fuse_ilookup(fc, nodeid, NULL); if (!inode) goto out_up_killsb; + if (!S_ISREG(inode->i_mode)) { + err =3D -EINVAL; + goto out_iput; + } =20 mapping =3D inode->i_mapping; file_size =3D i_size_read(inode); @@ -1966,7 +1970,10 @@ static int fuse_notify_retrieve(struct fuse_conn *fc= , unsigned int size, =20 inode =3D fuse_ilookup(fc, nodeid, &fm); if (inode) { - err =3D fuse_retrieve(fm, inode, &outarg); + if (!S_ISREG(inode->i_mode)) + err =3D -EINVAL; + else + err =3D fuse_retrieve(fm, inode, &outarg); iput(inode); } up_read(&fc->killsb); --- base-commit: ab5fce87a778cb780a05984a2ca448f2b41aafbf change-id: 20260519-fuse-dir-pagecache-382a54146826 -- =20 Jann Horn