From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4A57F319851; Sun, 7 Jun 2026 10:50:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780829421; cv=none; b=A9ppNZ+o1ShWsXN0lovZreat/HBwZuKG3y6gV6e2CUgaMUFAUtzupkd4VisJPy3plcMBr9ZbWp8u/m3bz1yOA8EsL3gfTKMlsDrjcJNbyXIuGV04mzaS/o4565vmT1+Ujn/BVIswK4jhr28VyYsEwSHIir1JRYUP9hqYEPh2WcE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780829421; c=relaxed/simple; bh=7I0q+kLxJxDyBUkO7kuUOUKIVjZmeWDteG0/HSLvB6k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jYShm3i1uirk9hgB0Q2rjYC1oNyj90elrliPcHf5yeT6mQjOKyzGc3zR9pCcI5pJJPV8sTcL2+8amsd/etIkeA0jt28kmXYbfpLGXOHtTRpoGzPqq04ZjvL7pBTx3DAQYYiDAGPydfNeiUraTrzApoyhmOjPpm1XyHnO89Lj5h8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wDc40h57; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="wDc40h57" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D70B1F00893; Sun, 7 Jun 2026 10:50:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780829420; bh=u9z3L1ilCzH2eSmRaHJgTkKaKdJkXSsT+OITud1scQg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=wDc40h57oMNGri59MI6NIfGZfOIoCyQWQRPfB1HQMjMSB+mlHAcEXl1RMyWDMuoda QJBvIiOeMqlB5+S6YZaI4EPuC7dhR3VZUNqvNEhgxMUEEWSVQ+QmdH+Wox8H4XBoRU faaXHIN01joJYx95leCM4zGeRNP+fz70mHyf5qZk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable , Michael Bommarito Subject: [PATCH 6.18 246/315] usb: gadget: f_fs: copy only received bytes on short ep0 read Date: Sun, 7 Jun 2026 12:00:33 +0200 Message-ID: <20260607095736.597744723@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095727.528828913@linuxfoundation.org> References: <20260607095727.528828913@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael Bommarito commit 4e036c10e7f4df5d951c69cc3697bc8e209c6d02 upstream. ffs_ep0_read() allocates its control-OUT data buffer with kmalloc() (not kzalloc) at the Length value from the Setup packet, then copies that full len to userspace regardless of how many bytes were actually received: data = kmalloc(len, GFP_KERNEL); ... ret = __ffs_ep0_queue_wait(ffs, data, len); if ((ret > 0) && (copy_to_user(buf, data, len))) ret = -EFAULT; __ffs_ep0_queue_wait() returns req->actual, which on a short control OUT transfer is strictly less than len. The copy_to_user() call still copies len bytes, so on a short OUT the last (len - ret) bytes of the kmalloc() buffer -- uninitialised slab residue -- are delivered to the FunctionFS daemon. Short ep0 OUT completions are specified USB control-transfer behavior and are produced by in-tree UDCs: * dwc2 continues on req->actual < req->length for ep0 DATA OUT (short-not-ok is the only ep0-OUT stall path). * aspeed_udc ends ep0 OUT on rx_len < ep->ep.maxpacket. * renesas_usbf logs "ep0 short packet" and completes the request. * dwc3 stalls on short IN but not on short OUT. A short ep0 OUT is therefore not evidence of a broken UDC; it is a normal condition f_fs has to cope with. The sibling gadgetfs implementation in drivers/usb/gadget/legacy/inode.c already does this correctly via min(len, dev->req->actual) before copy_to_user(). This patch brings f_fs.c to the same safe pattern rather than trimming at a defensive layer. The bug is reached from the FunctionFS device node, which in real deployments is owned by the privileged gadget daemon (adbd, UMS, composite gadget services, etc.); it is not reachable from unprivileged userspace. Linux host stacks normally reject short-wLength control OUTs before they reach the gadget, so reproducing this required a build that bypasses that host-side check. With the bypass in place, a 1-byte payload on a 64-byte Setup produces 63 bytes of non-canary slab residue in the daemon's read buffer. Fix by copying only ret (actually received) bytes to userspace. Fixes: ddf8abd25994 ("USB: f_fs: the FunctionFS driver") Cc: stable Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Michael Bommarito Link: https://patch.msgid.link/20260419160359.1577270-1-michael.bommarito@gmail.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/function/f_fs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -622,7 +622,7 @@ static ssize_t ffs_ep0_read(struct file /* unlocks spinlock */ ret = __ffs_ep0_queue_wait(ffs, data, len); - if ((ret > 0) && (copy_to_user(buf, data, len))) + if ((ret > 0) && (copy_to_user(buf, data, ret))) ret = -EFAULT; goto done_mutex;