[PATCH 6.12 08/77] netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells@redhat.com>

commit dbe556972100fabb8e5a1b3d2163831ff07b1e8e upstream.

netfs_unlock_abandoned_read_pages(rreq) accesses the index of the folios it
is wanting to unlock and compares that to rreq->no_unlock_folio so that it
doesn't unlock a folio being read for netfs_perform_write() or
netfs_write_begin().

However, given that netfs_unlock_abandoned_read_pages() is called _after_
NETFS_RREQ_IN_PROGRESS is cleared, the one folio that it's not allowed to
dereference is the one specified by ->no_unlock_folio as ownership
immediately reverts to the caller.

Fix this by storing the folio pointer instead and using that rather than
the index.  Also fix netfs_unlock_read_folio() where the same applies.

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Closes: https://sashiko.dev/#/patchset/20260414082004.3756080-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260512123404.719402-20-dhowells@redhat.com
cc: Paulo Alcantara <pc@manguebit.org>
cc: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Shishkin Aleksey <demonaxsh@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/netfs/buffered_read.c |    4 ++--
 fs/netfs/read_collect.c  |    2 +-
 fs/netfs/read_retry.c    |    2 +-
 include/linux/netfs.h    |    2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -734,7 +734,7 @@ retry:
 		ret = PTR_ERR(rreq);
 		goto error;
 	}
-	rreq->no_unlock_folio	= folio->index;
+	rreq->no_unlock_folio	= folio;
 	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
 
 	ret = netfs_begin_cache_read(rreq, ctx);
@@ -800,7 +800,7 @@ int netfs_prefetch_for_write(struct file
 		goto error;
 	}
 
-	rreq->no_unlock_folio = folio->index;
+	rreq->no_unlock_folio = folio;
 	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
 	ret = netfs_begin_cache_read(rreq, ctx);
 	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -73,7 +73,7 @@ static void netfs_unlock_read_folio(stru
 	}
 
 	if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
-		if (folio->index == rreq->no_unlock_folio &&
+		if (folio == rreq->no_unlock_folio &&
 		    test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags)) {
 			_debug("no unlock");
 		} else {
--- a/fs/netfs/read_retry.c
+++ b/fs/netfs/read_retry.c
@@ -249,7 +249,7 @@ void netfs_unlock_abandoned_read_pages(s
 			struct folio *folio = folioq_folio(p, slot);
 
 			if (folio && !folioq_is_marked2(p, slot)) {
-				if (folio->index == rreq->no_unlock_folio &&
+				if (folio == rreq->no_unlock_folio &&
 				    test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO,
 					     &rreq->flags)) {
 					_debug("no unlock");
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -266,7 +266,7 @@ struct netfs_io_request {
 	atomic64_t		issued_to;	/* Write issuer folio cursor */
 	unsigned long long	collected_to;	/* Point we've collected to */
 	unsigned long long	cleaned_to;	/* Position we've cleaned folios to */
-	pgoff_t			no_unlock_folio; /* Don't unlock this folio after read */
+	const struct folio	*no_unlock_folio; /* Don't unlock this folio after read */
 	size_t			prev_donated;	/* Fallback for subreq->prev_donated */
 	refcount_t		ref;
 	unsigned long		flags;