From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 AF4E71C93B7; Tue, 27 Aug 2024 15:16:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724771796; cv=none; b=bEo52CrxZC9oiQCYcv0j7jyNRdUJU+3xCdxYgTu2hZ+a8g4YFs2ldTWHY5vyYKkAnmq3s8UfrNTTUWczh1+buxFS5E03o00LdhMGZ804X5bMd00kLHTVneHKGkJPQTLzipVDfFkY1IQz10QPUcFw6IHkHP7UayYMuxzm4j0KVFY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724771796; c=relaxed/simple; bh=UYNhqfSuAWIP7b0GclDAdbpRsOfVoKJ3u1PHAOmQtvA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=W3AXnM800uRHkZ/xrVcVZrcrdUlVP27wD3N4zgQjpowTadD8PmCOlBwBTWL3sCEvDqCTOD0nkSAwjhFqcVSV6kol3oBM2MbOvFYHKvLInvR392hHLhdc2ghp12yYOFf4knPC4UI8k2GVirYkiFmmvPKGm506ALAnL53unifnUQA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=aJFeOypR; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="aJFeOypR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19E22C4DE18; Tue, 27 Aug 2024 15:16:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1724771796; bh=UYNhqfSuAWIP7b0GclDAdbpRsOfVoKJ3u1PHAOmQtvA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aJFeOypR3ePFORlWp+nVy/JH6gixPMIzRXXlTtONWP7B1E7dCQNiExoLiw/mRbJKf 9dn2a4SB39f9p3UTTmHbmsjbALYhyC3wqpxF8c7KQhoKzrOkKDhC6QR2q5qC2WBRfx p8NJRUi4gDOBCDy3GCBBzc0SpjYqrIVlsYS+q0WI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Max Kellermann , David Howells , Jeff Layton , netfs@lists.linux.dev, linux-fsdevel@vger.kernel.org, Christian Brauner Subject: [PATCH 6.1 023/321] fs/netfs/fscache_cookie: add missing "n_accesses" check Date: Tue, 27 Aug 2024 16:35:31 +0200 Message-ID: <20240827143839.094187208@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240827143838.192435816@linuxfoundation.org> References: <20240827143838.192435816@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Max Kellermann commit f71aa06398aabc2e3eaac25acdf3d62e0094ba70 upstream. This fixes a NULL pointer dereference bug due to a data race which looks like this: BUG: kernel NULL pointer dereference, address: 0000000000000008 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 33 PID: 16573 Comm: kworker/u97:799 Not tainted 6.8.7-cm4all1-hp+ #43 Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/17/2018 Workqueue: events_unbound netfs_rreq_write_to_cache_work RIP: 0010:cachefiles_prepare_write+0x30/0xa0 Code: 57 41 56 45 89 ce 41 55 49 89 cd 41 54 49 89 d4 55 53 48 89 fb 48 83 ec 08 48 8b 47 08 48 83 7f 10 00 48 89 34 24 48 8b 68 20 <48> 8b 45 08 4c 8b 38 74 45 49 8b 7f 50 e8 4e a9 b0 ff 48 8b 73 10 RSP: 0018:ffffb4e78113bde0 EFLAGS: 00010286 RAX: ffff976126be6d10 RBX: ffff97615cdb8438 RCX: 0000000000020000 RDX: ffff97605e6c4c68 RSI: ffff97605e6c4c60 RDI: ffff97615cdb8438 RBP: 0000000000000000 R08: 0000000000278333 R09: 0000000000000001 R10: ffff97605e6c4600 R11: 0000000000000001 R12: ffff97605e6c4c68 R13: 0000000000020000 R14: 0000000000000001 R15: ffff976064fe2c00 FS: 0000000000000000(0000) GS:ffff9776dfd40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3: 000000005942c002 CR4: 00000000001706f0 Call Trace: ? __die+0x1f/0x70 ? page_fault_oops+0x15d/0x440 ? search_module_extables+0xe/0x40 ? fixup_exception+0x22/0x2f0 ? exc_page_fault+0x5f/0x100 ? asm_exc_page_fault+0x22/0x30 ? cachefiles_prepare_write+0x30/0xa0 netfs_rreq_write_to_cache_work+0x135/0x2e0 process_one_work+0x137/0x2c0 worker_thread+0x2e9/0x400 ? __pfx_worker_thread+0x10/0x10 kthread+0xcc/0x100 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x30/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1b/0x30 Modules linked in: CR2: 0000000000000008 ---[ end trace 0000000000000000 ]--- This happened because fscache_cookie_state_machine() was slow and was still running while another process invoked fscache_unuse_cookie(); this led to a fscache_cookie_lru_do_one() call, setting the FSCACHE_COOKIE_DO_LRU_DISCARD flag, which was picked up by fscache_cookie_state_machine(), withdrawing the cookie via cachefiles_withdraw_cookie(), clearing cookie->cache_priv. At the same time, yet another process invoked cachefiles_prepare_write(), which found a NULL pointer in this code line: struct cachefiles_object *object = cachefiles_cres_object(cres); The next line crashes, obviously: struct cachefiles_cache *cache = object->volume->cache; During cachefiles_prepare_write(), the "n_accesses" counter is non-zero (via fscache_begin_operation()). The cookie must not be withdrawn until it drops to zero. The counter is checked by fscache_cookie_state_machine() before switching to FSCACHE_COOKIE_STATE_RELINQUISHING and FSCACHE_COOKIE_STATE_WITHDRAWING (in "case FSCACHE_COOKIE_STATE_FAILED"), but not for FSCACHE_COOKIE_STATE_LRU_DISCARDING ("case FSCACHE_COOKIE_STATE_ACTIVE"). This patch adds the missing check. With a non-zero access counter, the function returns and the next fscache_end_cookie_access() call will queue another fscache_cookie_state_machine() call to handle the still-pending FSCACHE_COOKIE_DO_LRU_DISCARD. Fixes: 12bb21a29c19 ("fscache: Implement cookie user counting and resource pinning") Signed-off-by: Max Kellermann Signed-off-by: David Howells Link: https://lore.kernel.org/r/20240729162002.3436763-2-dhowells@redhat.com cc: Jeff Layton cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org cc: stable@vger.kernel.org Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman --- fs/fscache/cookie.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/fs/fscache/cookie.c +++ b/fs/fscache/cookie.c @@ -741,6 +741,10 @@ again_locked: spin_lock(&cookie->lock); } if (test_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags)) { + if (atomic_read(&cookie->n_accesses) != 0) + /* still being accessed: postpone it */ + break; + __fscache_set_cookie_state(cookie, FSCACHE_COOKIE_STATE_LRU_DISCARDING); wake = true;