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 82D79386571; Tue, 21 Jul 2026 17:50:28 +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=1784656229; cv=none; b=Jj80v09cWzaMlmr2HGhJqnSaXXugQ7+Jx4IbxquGEvMk/OQBtD6ExfN9itwVz/zwibPCiJCYpu4qUht58Gh9tId+0C+8ctJ9uRR+dl4889eXKThinNrFoVGOzq9dkGyrWwCaZ6Q1w5hXhqcK7i4d6hn38zDNDo72odWnH4V3hZk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784656229; c=relaxed/simple; bh=NcjoReEUDcvNdYc5qWajqJP+pk1xDSbtpIEXP/ujYtw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SDbSCaAOUALzd+MXZECdetqt9+YTXnSBLSSrgEJWUB0zv8JBCY1YmBIHRd1t84HsuJ+QrdtPxkeYqaSRFeL5TySPi9PyCwiUk6RkZIOXAuKSOsXXQhNhk1SDo/H98CVKJPL4w4A8p2VBQr4P4eLDYtZETulFCptiE0ejWVx6Yic= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Pajd2XA4; 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="Pajd2XA4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA5421F000E9; Tue, 21 Jul 2026 17:50:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784656228; bh=dTna4z//bSqT1rs7NSuI8sQYgLyOp3lamSxO8B1wxto=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Pajd2XA4WNGLrfIvb02IxZy/mD4WTRW5om+hoQGfoH8wne5LUwJ3Deb3cGoIj6ir5 XJ6wWo5sqNdZGbUHoxc5dkCDuorITWNqsywCNdBoFV8CNppgcl8znJrBed+Nq8MLQ8 DFfhnylTBrJ7RiE+s9iR5E8HnTmudpcYnv20SSv0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+36e50496c8ac4bcde3f9@syzkaller.appspotmail.com, Al Viro , Deepanshu Kartikey , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.18 0308/1611] bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs Date: Tue, 21 Jul 2026 17:07:04 +0200 Message-ID: <20260721152522.003732236@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152514.750365251@linuxfoundation.org> References: <20260721152514.750365251@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: Deepanshu Kartikey [ Upstream commit b93c55b4932dd7e32dca8cf34a3443cc87a02906 ] commit 4f375ade6aa9 ("bpf: Avoid RCU context warning when unpinning htab with internal structs") moved inode cleanup from ->free_inode() into ->destroy_inode() to avoid sleeping in RCU context when calling bpf_any_put(). However this removed the RCU delay on freeing the inode itself and the cached symlink body (i_link), both of which can be accessed by RCU pathwalk (pick_link, may_lookup etc.). This causes a use-after-free when a concurrent unlinkat() drops the last inode reference and destroy_inode() frees the inode immediately, while another task is still walking the path in RCU mode and reads inode->i_opflags (offset +2) inside current_time() -> is_mgtime(). KASAN reports: BUG: KASAN: slab-use-after-free in is_mgtime include/linux/fs.h:2313 Read of size 2 at addr ffff8880407e4282 (offset +2 = i_opflags) The rules (per Al Viro): ->destroy_inode() called immediately, can sleep, use for blocking cleanup e.g. bpf_any_put() ->free_inode() called after RCU grace period, use for freeing inode and anything RCU-accessible e.g. i_link Fix: split the two concerns properly: - keep bpf_any_put() in bpf_destroy_inode() since it is blocking and needs to run promptly - introduce bpf_free_inode() to handle kfree(i_link) and free_inode_nonrcu() with proper RCU delay, preventing the UAF Fixes: 4f375ade6aa9 ("bpf: Avoid RCU context warning when unpinning htab with internal structs") Reported-by: syzbot+36e50496c8ac4bcde3f9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=36e50496c8ac4bcde3f9 Suggested-by: Al Viro Link: https://lore.kernel.org/all/20260423043906.GN3518998@ZenIV/ Link: https://lore.kernel.org/all/20260602002607.110866-1-kartikey406@gmail.com/T/ [v1] Signed-off-by: Deepanshu Kartikey Acked-by: Al Viro Link: https://lore.kernel.org/r/20260602025249.113828-1-kartikey406@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/inode.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c index 81780bcf8d2544..cf907fab3721f1 100644 --- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -779,10 +779,18 @@ static void bpf_destroy_inode(struct inode *inode) { enum bpf_type type; - if (S_ISLNK(inode->i_mode)) - kfree(inode->i_link); if (!bpf_inode_type(inode, &type)) bpf_any_put(inode->i_private, type); +} + +/* + * Called after RCU grace period - safe to free inode and anything + * that might be accessed by RCU pathwalk (inode fields, i_link). + */ +static void bpf_free_inode(struct inode *inode) +{ + if (S_ISLNK(inode->i_mode)) + kfree(inode->i_link); free_inode_nonrcu(inode); } @@ -791,6 +799,7 @@ const struct super_operations bpf_super_ops = { .drop_inode = inode_just_drop, .show_options = bpf_show_options, .destroy_inode = bpf_destroy_inode, + .free_inode = bpf_free_inode, }; enum { -- 2.53.0