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Thu, 17 Sep 2026 06:53:44 -0700 (PDT) Received: from localhost.localdomain ([2409:8a1e:2e81:7320:2428:17da:9062:91b2]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e360ddfc2sm5303334a91.16.2026.09.17.06.53.42 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 17 Sep 2026 06:53:44 -0700 (PDT) From: zjamg To: Greg Kroah-Hartman Cc: Michal Nazarewicz , Robert Baldyga , Felipe Balbi , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, zjamg Subject: [PATCH 0/1] usb: gadget: f_fs: fix NULL pointer dereference in FUNCTIONFS_ENDPOINT_DESC Date: Thu, 17 Sep 2026 21:53:36 +0800 Message-ID: <20260917135337.65444-1-ndaugoing@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi, This patch addresses a kernel NULL pointer dereference panic in FunctionFS when calling the FUNCTIONFS_ENDPOINT_DESC ioctl. In FunctionFS, user space can legitimately supply only a subset of speed descriptors (e.g., only full-speed descriptors via FUNCTIONFS_HAS_FS_DESC). When the USB gadget is subsequently connected to a high-speed or super-speed host: 1. composite.c:config_ep_by_speed() detects that the function lacks descriptors for the current speed and gracefully falls back to full-speed descriptors (f->fs_descriptors). 2. The endpoint is enabled via usb_ep_enable(), and epfile->ep becomes valid. 3. However, when user space calls ioctl(fd, FUNCTIONFS_ENDPOINT_DESC), ffs_epfile_ioctl() selects the descriptor index solely based on epfile->ffs->gadget->speed (desc_idx = 1 for HIGH, 2 for SUPER/SUPER_PLUS). 4. Because user space only supplied full-speed descriptors, epfile->ep->descs[desc_idx] is NULL. 5. The subsequent memcpy(&desc1, desc, desc->bLength) immediately dereferences the NULL pointer, causing an instant kernel crash: [ 2.154836] Call trace: [ 2.154836] ffs_epfile_ioctl+0xe14/0x2c40 [usb_f_fs] (P) [ 2.155003] __arm64_sys_ioctl+0x128/0x1a4 [ 2.155298] invoke_syscall.constprop.0+0x64/0x260 [ 2.155374] el0_svc_common.constprop.0+0xa0/0x240 [ 2.155441] do_el0_svc+0x3c/0x60 [ 2.155494] el0_svc+0x38/0x98 [ 2.155547] el0t_64_sync_handler+0xa0/0xe4 [ 2.155606] el0t_64_sync+0x198/0x19c [ 2.156463] Kernel panic - not syncing: Oops: Fatal exception The fix restores the speed fallback loop mirroring config_ep_by_speed() and historical f_fs behavior, defensively checks epfile->ep->ep->desc as a fallback, and returns -EINVAL safely if no valid descriptor is found. Testing with QEMU ARM64 using dummy_hcd confirms that after applying this patch, the ioctl succeeds and returns the fallback descriptor cleanly without any crash. zjamg (1): usb: gadget: f_fs: Fix NULL pointer dereference in FUNCTIONFS_ENDPOINT_DESC drivers/usb/gadget/function/f_fs.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) -- 2.53.0