From: David Howells Date: Tue, 12 May 2026 12:33:54 +0000 (+0100) Subject: netfs: Fix early put of sink folio in netfs_read_gaps() X-Git-Tag: v6.12.92~78 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=2a39d49c8d97df8cb8fa80c10859bc1ba7358c6b;p=thirdparty%2Fkernel%2Fstable.git netfs: Fix early put of sink folio in netfs_read_gaps() [ Upstream commit 3e5dd91b87a8b1450217b56a336bee315f40da7d ] Fix netfs_read_gaps() to release the sink page it uses after waiting for the request to complete. The way the sink page is used is that an ITER_BVEC-class iterator is created that has the gaps from the target folio at either end, but has the sink page tiled over the middle so that a single read op can fill in both gaps. The bug was found by KASAN detecting a UAF on the generic/075 xfstest in the cifsd kernel thread that handles reception of data from the TCP socket: BUG: KASAN: use-after-free in _copy_to_iter+0x48a/0xa20 Write of size 885 at addr ffff888107f92000 by task cifsd/1285 CPU: 2 UID: 0 PID: 1285 Comm: cifsd Not tainted 7.0.0 #6 PREEMPT(lazy) Call Trace: dump_stack_lvl+0x5d/0x80 print_report+0x17f/0x4f1 kasan_report+0x100/0x1e0 kasan_check_range+0x10f/0x1e0 __asan_memcpy+0x3c/0x60 _copy_to_iter+0x48a/0xa20 __skb_datagram_iter+0x2c9/0x430 skb_copy_datagram_iter+0x6e/0x160 tcp_recvmsg_locked+0xce0/0x1130 tcp_recvmsg+0xeb/0x300 inet_recvmsg+0xcf/0x3a0 sock_recvmsg+0xea/0x100 cifs_readv_from_socket+0x3a6/0x4d0 [cifs] cifs_read_iter_from_socket+0xdd/0x130 [cifs] cifs_readv_receive+0xaad/0xb10 [cifs] cifs_demultiplex_thread+0x1148/0x1740 [cifs] kthread+0x1cf/0x210 Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading") Reported-by: Steve French Signed-off-by: David Howells Link: https://patch.msgid.link/20260512123404.719402-18-dhowells@redhat.com Reviewed-by: Paulo Alcantara (Red Hat) cc: Paulo Alcantara cc: Matthew Wilcox cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c index 2dd2260352db..1c906035fef0 100644 --- a/fs/netfs/buffered_read.c +++ b/fs/netfs/buffered_read.c @@ -525,14 +525,14 @@ static int netfs_read_gaps(struct file *file, struct folio *folio) netfs_read_to_pagecache(rreq); - if (sink) - folio_put(sink); - ret = netfs_wait_for_read(rreq); if (ret == 0) { flush_dcache_folio(folio); folio_mark_uptodate(folio); } + + if (sink) + folio_put(sink); folio_unlock(folio); netfs_put_request(rreq, false, netfs_rreq_trace_put_return); return ret < 0 ? ret : 0;