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netfs: Fix potential UAF in netfs_unlock_abandoned_read_pages()

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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: ee4cdf7ba8 ("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>
This commit is contained in:
David Howells 2026-05-12 13:33:56 +01:00 committed by Christian Brauner
parent 5046a34f06
commit dbe5569721
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
4 changed files with 5 additions and 5 deletions
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4
fs/netfs/buffered_read.c
View File

@ -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)

2
fs/netfs/read_collect.c
View File

@ -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 {

2
fs/netfs/read_retry.c
View File

@ -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");

2
include/linux/netfs.h
View File

@ -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) */