[PATCH v5 19/24] netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages()

David Howells
2026-04-28T13:19:41Z

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>
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
---
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(-)

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index db279124d450..89ae5241c49c 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -670,7 +670,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
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);
@@ -736,7 +736,7 @@ int netfs_prefetch_for_write(struct file *file, struct folio *folio,
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)
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index 3c9b847885c2..23660a590124 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -83,7 +83,7 @@ static void netfs_unlock_read_folio(struct netfs_io_request *rreq,
}

just_unlock:
- 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 {
diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
index e10eb5a07332..f59a70f3a086 100644
--- a/fs/netfs/read_retry.c
+++ b/fs/netfs/read_retry.c
@@ -292,7 +292,7 @@ void netfs_unlock_abandoned_read_pages(struct netfs_io_request *rreq)
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");
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 1b1db8e6cdf1..9a68bee01c1a 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -252,7 +252,7 @@ struct netfs_io_request {
unsigned long long collected_to; /* Point we've collected to */
unsigned long long cleaned_to; /* Position we've cleaned folios to */
unsigned long long abandon_to; /* Position to abandon 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 */
unsigned int direct_bv_count; /* Number of elements in direct_bv[] */
unsigned int debug_id;
unsigned int rsize; /* Maximum read size (0 for none) */