* [PATCH 6.1.y 0/9] eventpoll: fix ep_remove struct eventpoll / struct file UAF
2026-06-28 14:20 ` Salvatore Bonaccorso
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 1/9] eventpoll: don't decrement ep refcount while still holding the ep mutex Wentao Guan
` (9 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil; +Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable
Fixes CVE-2026-46242 eventpoll: fix ep_remove struct eventpoll / struct file UAF
base on link: https://lore.kernel.org/stable/20260619-6-12-cve-2026-46242-v1-0-e15a6de43c11@cherry.de/
add commit ("file: add fput() cleanup helper") to fix build error in v6.6.y :
error: cleanup argument not a function
struct file *file __free(fput) = NULL;
add commit ("eventpoll: don't decrement ep refcount while still holding the ep mutex")
to fix context different in v6.1.y
Christian Brauner (8):
file: add fput() cleanup helper
eventpoll: use hlist_is_singular_node() in __ep_remove()
eventpoll: split __ep_remove()
eventpoll: kill __ep_remove()
eventpoll: drop vestigial __ prefix from ep_remove_{file,epi}()
eventpoll: rename ep_remove_safe() back to ep_remove()
eventpoll: move epi_fget() up
eventpoll: fix ep_remove struct eventpoll / struct file UAF
Linus Torvalds (1):
eventpoll: don't decrement ep refcount while still holding the ep
mutex
fs/eventpoll.c | 152 +++++++++++++++++++++++--------------------
include/linux/file.h | 2 +
2 files changed, 85 insertions(+), 69 deletions(-)
--
2.30.2
^ permalink raw reply [flat|nested] 22+ messages in thread* [PATCH 6.1.y 1/9] eventpoll: don't decrement ep refcount while still holding the ep mutex
2026-06-28 14:20 ` Salvatore Bonaccorso
2026-06-28 16:19 ` [PATCH 6.1.y 0/9] " Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 2/9] file: add fput() cleanup helper Wentao Guan
` (8 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Linus Torvalds, Jann Horn, Alexander Viro, Jan Kara
From: Linus Torvalds <torvalds@linux-foundation.org>
commit 8c2e52ebbe885c7eeaabd3b7ddcdc1246fc400d2 upstream.
Jann Horn points out that epoll is decrementing the ep refcount and then
doing a
mutex_unlock(&ep->mtx);
afterwards. That's very wrong, because it can lead to a use-after-free.
That pattern is actually fine for the very last reference, because the
code in question will delay the actual call to "ep_free(ep)" until after
it has unlocked the mutex.
But it's wrong for the much subtler "next to last" case when somebody
*else* may also be dropping their reference and free the ep while we're
still using the mutex.
Note that this is true even if that other user is also using the same ep
mutex: mutexes, unlike spinlocks, can not be used for object ownership,
even if they guarantee mutual exclusion.
A mutex "unlock" operation is not atomic, and as one user is still
accessing the mutex as part of unlocking it, another user can come in
and get the now released mutex and free the data structure while the
first user is still cleaning up.
See our mutex documentation in Documentation/locking/mutex-design.rst,
in particular the section [1] about semantics:
"mutex_unlock() may access the mutex structure even after it has
internally released the lock already - so it's not safe for
another context to acquire the mutex and assume that the
mutex_unlock() context is not using the structure anymore"
So if we drop our ep ref before the mutex unlock, but we weren't the
last one, we may then unlock the mutex, another user comes in, drops
_their_ reference and releases the 'ep' as it now has no users - all
while the mutex_unlock() is still accessing it.
Fix this by simply moving the ep refcount dropping to outside the mutex:
the refcount itself is atomic, and doesn't need mutex protection (that's
the whole _point_ of refcounts: unlike mutexes, they are inherently
about object lifetimes).
Reported-by: Jann Horn <jannh@google.com>
Link: https://docs.kernel.org/locking/mutex-design.html#semantics [1]
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 521e9ff0b67c66a17d6f9593dfccafaa984aae4c)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index f6038819fe79f..7ca1b5931480c 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -777,7 +777,7 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
call_rcu(&epi->rcu, epi_rcu_free);
percpu_counter_dec(&ep->user->epoll_watches);
- return ep_refcount_dec_and_test(ep);
+ return true;
}
/*
@@ -785,14 +785,14 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
*/
static void ep_remove_safe(struct eventpoll *ep, struct epitem *epi)
{
- WARN_ON_ONCE(__ep_remove(ep, epi, false));
+ if (__ep_remove(ep, epi, false))
+ WARN_ON_ONCE(ep_refcount_dec_and_test(ep));
}
static void ep_clear_and_put(struct eventpoll *ep)
{
struct rb_node *rbp, *next;
struct epitem *epi;
- bool dispose;
/* We need to release all tasks waiting for these file */
if (waitqueue_active(&ep->poll_wait))
@@ -825,10 +825,8 @@ static void ep_clear_and_put(struct eventpoll *ep)
cond_resched();
}
- dispose = ep_refcount_dec_and_test(ep);
mutex_unlock(&ep->mtx);
-
- if (dispose)
+ if (ep_refcount_dec_and_test(ep))
ep_free(ep);
}
@@ -1008,7 +1006,7 @@ void eventpoll_release_file(struct file *file)
dispose = __ep_remove(ep, epi, true);
mutex_unlock(&ep->mtx);
- if (dispose)
+ if (dispose && ep_refcount_dec_and_test(ep))
ep_free(ep);
goto again;
}
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 2/9] file: add fput() cleanup helper
2026-06-28 14:20 ` Salvatore Bonaccorso
2026-06-28 16:19 ` [PATCH 6.1.y 0/9] " Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 1/9] eventpoll: don't decrement ep refcount while still holding the ep mutex Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 3/9] eventpoll: use hlist_is_singular_node() in __ep_remove() Wentao Guan
` (7 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Josef Bacik, Jeff Layton
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit 257b1c2c78c25643526609dee0c15f1544eb3252 ]
Add a simple helper to put a file reference.
Link: https://lore.kernel.org/r/20240719-work-mount-namespace-v1-4-834113cab0d2@kernel.org
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
(cherry picked from commit 257b1c2c78c25643526609dee0c15f1544eb3252)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
include/linux/file.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/include/linux/file.h b/include/linux/file.h
index 6e9099d293436..221ba0888107a 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -11,6 +11,7 @@
#include <linux/posix_types.h>
#include <linux/errno.h>
#include <linux/cleanup.h>
+#include <linux/err.h>
struct file;
@@ -93,6 +94,7 @@ extern void put_unused_fd(unsigned int fd);
DEFINE_CLASS(get_unused_fd, int, if (_T >= 0) put_unused_fd(_T),
get_unused_fd_flags(flags), unsigned flags)
+DEFINE_FREE(fput, struct file *, if (!IS_ERR_OR_NULL(_T)) fput(_T))
extern void fd_install(unsigned int fd, struct file *file);
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 3/9] eventpoll: use hlist_is_singular_node() in __ep_remove()
2026-06-28 14:20 ` Salvatore Bonaccorso
` (2 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 2/9] file: add fput() cleanup helper Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 4/9] eventpoll: split __ep_remove() Wentao Guan
` (6 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Quentin Schulz
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit 3d9fd0abc94d8cd430cc7cd7d37ce5e5aae2cd2b ]
Replace the open-coded "epi is the only entry in file->f_ep" check
with hlist_is_singular_node(). Same semantics, and the helper avoids
the head-cacheline access in the common false case.
Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-1-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 7ca1b5931480c..bc605ad291499 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -745,7 +745,7 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
to_free = NULL;
head = file->f_ep;
- if (head->first == &epi->fllink && !epi->fllink.next) {
+ if (hlist_is_singular_node(&epi->fllink, head)) {
/* See eventpoll_release() for details. */
WRITE_ONCE(file->f_ep, NULL);
if (!is_file_epoll(file)) {
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 4/9] eventpoll: split __ep_remove()
2026-06-28 14:20 ` Salvatore Bonaccorso
` (3 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 3/9] eventpoll: use hlist_is_singular_node() in __ep_remove() Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 5/9] eventpoll: kill __ep_remove() Wentao Guan
` (5 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Linus Torvalds, Quentin Schulz
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit 0f7bdfd413000985de09fc39eb9efa1e091a3ce0 ]
Split __ep_remove() to delineate file removal from epoll item removal.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-2-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index bc605ad291499..9e728b359ea3d 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -715,6 +715,9 @@ static void ep_free(struct eventpoll *ep)
kfree_rcu(ep, rcu);
}
+static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi, struct file *file);
+static bool __ep_remove_epi(struct eventpoll *ep, struct epitem *epi);
+
/*
* Removes a "struct epitem" from the eventpoll RB tree and deallocates
* all the associated resources. Must be called with "mtx" held.
@@ -726,8 +729,6 @@ static void ep_free(struct eventpoll *ep)
static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
{
struct file *file = epi->ffd.file;
- struct epitems_head *to_free;
- struct hlist_head *head;
lockdep_assert_irqs_enabled();
@@ -743,8 +744,21 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
return false;
}
- to_free = NULL;
- head = file->f_ep;
+ __ep_remove_file(ep, epi, file);
+ return __ep_remove_epi(ep, epi);
+}
+
+/*
+ * Called with &file->f_lock held,
+ * returns with it released
+ */
+static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi, struct file *file)
+{
+ struct epitems_head *to_free = NULL;
+ struct hlist_head *head = file->f_ep;
+
+ lockdep_assert_held(&ep->mtx);
+
if (hlist_is_singular_node(&epi->fllink, head)) {
/* See eventpoll_release() for details. */
WRITE_ONCE(file->f_ep, NULL);
@@ -758,6 +772,11 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
hlist_del_rcu(&epi->fllink);
spin_unlock(&file->f_lock);
free_ephead(to_free);
+}
+
+static bool __ep_remove_epi(struct eventpoll *ep, struct epitem *epi)
+{
+ lockdep_assert_held(&ep->mtx);
rb_erase_cached(&epi->rbn, &ep->rbr);
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 5/9] eventpoll: kill __ep_remove()
2026-06-28 14:20 ` Salvatore Bonaccorso
` (4 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 4/9] eventpoll: split __ep_remove() Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 6/9] eventpoll: drop vestigial __ prefix from ep_remove_{file,epi}() Wentao Guan
` (4 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Quentin Schulz
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit e9e5cd40d7c403e19f21d0f7b8b8ba3a76b58330 ]
Remove the boolean conditional in __ep_remove() and restructure the code
so the check for racing with eventpoll_release_file() are only done in
the ep_remove_safe() path where they belong.
Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-3-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 67 ++++++++++++++++++++++----------------------------
1 file changed, 30 insertions(+), 37 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 9e728b359ea3d..93251a4858ed7 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -715,49 +715,18 @@ static void ep_free(struct eventpoll *ep)
kfree_rcu(ep, rcu);
}
-static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi, struct file *file);
-static bool __ep_remove_epi(struct eventpoll *ep, struct epitem *epi);
-
-/*
- * Removes a "struct epitem" from the eventpoll RB tree and deallocates
- * all the associated resources. Must be called with "mtx" held.
- * If the dying flag is set, do the removal only if force is true.
- * This prevents ep_clear_and_put() from dropping all the ep references
- * while running concurrently with eventpoll_release_file().
- * Returns true if the eventpoll can be disposed.
- */
-static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
-{
- struct file *file = epi->ffd.file;
-
- lockdep_assert_irqs_enabled();
-
- /*
- * Removes poll wait queue hooks.
- */
- ep_unregister_pollwait(ep, epi);
-
- /* Remove the current item from the list of epoll hooks */
- spin_lock(&file->f_lock);
- if (epi->dying && !force) {
- spin_unlock(&file->f_lock);
- return false;
- }
-
- __ep_remove_file(ep, epi, file);
- return __ep_remove_epi(ep, epi);
-}
-
/*
* Called with &file->f_lock held,
* returns with it released
*/
-static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi, struct file *file)
+static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi,
+ struct file *file)
{
struct epitems_head *to_free = NULL;
struct hlist_head *head = file->f_ep;
lockdep_assert_held(&ep->mtx);
+ lockdep_assert_held(&file->f_lock);
if (hlist_is_singular_node(&epi->fllink, head)) {
/* See eventpoll_release() for details. */
@@ -804,7 +773,25 @@ static bool __ep_remove_epi(struct eventpoll *ep, struct epitem *epi)
*/
static void ep_remove_safe(struct eventpoll *ep, struct epitem *epi)
{
- if (__ep_remove(ep, epi, false))
+ struct file *file = epi->ffd.file;
+
+ lockdep_assert_irqs_enabled();
+ lockdep_assert_held(&ep->mtx);
+
+ ep_unregister_pollwait(ep, epi);
+
+ /* sync with eventpoll_release_file() */
+ if (unlikely(READ_ONCE(epi->dying)))
+ return;
+
+ spin_lock(&file->f_lock);
+ if (epi->dying) {
+ spin_unlock(&file->f_lock);
+ return;
+ }
+ __ep_remove_file(ep, epi, file);
+
+ if (__ep_remove_epi(ep, epi))
WARN_ON_ONCE(ep_refcount_dec_and_test(ep));
}
@@ -1013,7 +1000,7 @@ void eventpoll_release_file(struct file *file)
spin_lock(&file->f_lock);
if (file->f_ep && file->f_ep->first) {
epi = hlist_entry(file->f_ep->first, struct epitem, fllink);
- epi->dying = true;
+ WRITE_ONCE(epi->dying, true);
spin_unlock(&file->f_lock);
/*
@@ -1022,7 +1009,13 @@ void eventpoll_release_file(struct file *file)
*/
ep = epi->ep;
mutex_lock(&ep->mtx);
- dispose = __ep_remove(ep, epi, true);
+
+ ep_unregister_pollwait(ep, epi);
+
+ spin_lock(&file->f_lock);
+ __ep_remove_file(ep, epi, file);
+ dispose = __ep_remove_epi(ep, epi);
+
mutex_unlock(&ep->mtx);
if (dispose && ep_refcount_dec_and_test(ep))
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 6/9] eventpoll: drop vestigial __ prefix from ep_remove_{file,epi}()
2026-06-28 14:20 ` Salvatore Bonaccorso
` (5 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 5/9] eventpoll: kill __ep_remove() Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 7/9] eventpoll: rename ep_remove_safe() back to ep_remove() Wentao Guan
` (3 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Quentin Schulz
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit 0feaf644f7180c4a91b6b405a881afbfd958f1cf ]
With __ep_remove() gone, the double-underscore on __ep_remove_file()
and __ep_remove_epi() no longer contrasts with a __-less parent and
just reads as noise. Rename both to ep_remove_file() and
ep_remove_epi(). No functional change.
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 93251a4858ed7..c63c2c46869e9 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -719,7 +719,7 @@ static void ep_free(struct eventpoll *ep)
* Called with &file->f_lock held,
* returns with it released
*/
-static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi,
+static void ep_remove_file(struct eventpoll *ep, struct epitem *epi,
struct file *file)
{
struct epitems_head *to_free = NULL;
@@ -743,7 +743,7 @@ static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi,
free_ephead(to_free);
}
-static bool __ep_remove_epi(struct eventpoll *ep, struct epitem *epi)
+static bool ep_remove_epi(struct eventpoll *ep, struct epitem *epi)
{
lockdep_assert_held(&ep->mtx);
@@ -789,9 +789,9 @@ static void ep_remove_safe(struct eventpoll *ep, struct epitem *epi)
spin_unlock(&file->f_lock);
return;
}
- __ep_remove_file(ep, epi, file);
+ ep_remove_file(ep, epi, file);
- if (__ep_remove_epi(ep, epi))
+ if (ep_remove_epi(ep, epi))
WARN_ON_ONCE(ep_refcount_dec_and_test(ep));
}
@@ -1013,8 +1013,8 @@ void eventpoll_release_file(struct file *file)
ep_unregister_pollwait(ep, epi);
spin_lock(&file->f_lock);
- __ep_remove_file(ep, epi, file);
- dispose = __ep_remove_epi(ep, epi);
+ ep_remove_file(ep, epi, file);
+ dispose = ep_remove_epi(ep, epi);
mutex_unlock(&ep->mtx);
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 7/9] eventpoll: rename ep_remove_safe() back to ep_remove()
2026-06-28 14:20 ` Salvatore Bonaccorso
` (6 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 6/9] eventpoll: drop vestigial __ prefix from ep_remove_{file,epi}() Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 8/9] eventpoll: move epi_fget() up Wentao Guan
` (2 subsequent siblings)
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Quentin Schulz
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit 0bade234723e40e4937be912e105785d6a51464e ]
The current name is just confusing and doesn't clarify anything.
Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-4-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index c63c2c46869e9..2a335dcb995c0 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -771,7 +771,7 @@ static bool ep_remove_epi(struct eventpoll *ep, struct epitem *epi)
/*
* ep_remove variant for callers owing an additional reference to the ep
*/
-static void ep_remove_safe(struct eventpoll *ep, struct epitem *epi)
+static void ep_remove(struct eventpoll *ep, struct epitem *epi)
{
struct file *file = epi->ffd.file;
@@ -818,7 +818,7 @@ static void ep_clear_and_put(struct eventpoll *ep)
/*
* Walks through the whole tree and try to free each "struct epitem".
- * Note that ep_remove_safe() will not remove the epitem in case of a
+ * Note that ep_remove() will not remove the epitem in case of a
* racing eventpoll_release_file(); the latter will do the removal.
* At this point we are sure no poll callbacks will be lingering around.
* Since we still own a reference to the eventpoll struct, the loop can't
@@ -827,7 +827,7 @@ static void ep_clear_and_put(struct eventpoll *ep)
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = next) {
next = rb_next(rbp);
epi = rb_entry(rbp, struct epitem, rbn);
- ep_remove_safe(ep, epi);
+ ep_remove(ep, epi);
cond_resched();
}
@@ -1505,21 +1505,21 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
mutex_unlock(&tep->mtx);
/*
- * ep_remove_safe() calls in the later error paths can't lead to
+ * ep_remove() calls in the later error paths can't lead to
* ep_free() as the ep file itself still holds an ep reference.
*/
ep_get(ep);
/* now check if we've created too many backpaths */
if (unlikely(full_check && reverse_path_check())) {
- ep_remove_safe(ep, epi);
+ ep_remove(ep, epi);
return -EINVAL;
}
if (epi->event.events & EPOLLWAKEUP) {
error = ep_create_wakeup_source(epi);
if (error) {
- ep_remove_safe(ep, epi);
+ ep_remove(ep, epi);
return error;
}
}
@@ -1543,7 +1543,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
* high memory pressure.
*/
if (unlikely(!epq.epi)) {
- ep_remove_safe(ep, epi);
+ ep_remove(ep, epi);
return -ENOMEM;
}
@@ -2222,7 +2222,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
* The eventpoll itself is still alive: the refcount
* can't go to zero here.
*/
- ep_remove_safe(ep, epi);
+ ep_remove(ep, epi);
error = 0;
} else {
error = -ENOENT;
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 8/9] eventpoll: move epi_fget() up
2026-06-28 14:20 ` Salvatore Bonaccorso
` (7 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 7/9] eventpoll: rename ep_remove_safe() back to ep_remove() Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:19 ` [PATCH 6.1.y 9/9] eventpoll: fix ep_remove struct eventpoll / struct file UAF Wentao Guan
2026-06-28 16:34 ` [PATCH 6.6.y 0/8] " Wentao Guan
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Quentin Schulz
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit 86e87059e6d1fd5115a31949726450ed03c1073b ]
We'll need it when removing files so move it up. No functional change.
Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-5-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
[file_ref_get(&file->f_ref) from original commit left as
atomic_long_inc_not_zero(&file->f_count) due to v6.12.y missing commit
90ee6ed776c0 ("fs: port files to file_ref") and its dependent commit
08ef26ea9ab3 ("fs: add file_ref")]
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 56 +++++++++++++++++++++++++-------------------------
1 file changed, 28 insertions(+), 28 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 2a335dcb995c0..67ba8bf17b800 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -715,6 +715,34 @@ static void ep_free(struct eventpoll *ep)
kfree_rcu(ep, rcu);
}
+/*
+ * The ffd.file pointer may be in the process of being torn down due to
+ * being closed, but we may not have finished eventpoll_release() yet.
+ *
+ * Normally, even with the atomic_long_inc_not_zero, the file may have
+ * been free'd and then gotten re-allocated to something else (since
+ * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU).
+ *
+ * But for epoll, users hold the ep->mtx mutex, and as such any file in
+ * the process of being free'd will block in eventpoll_release_file()
+ * and thus the underlying file allocation will not be free'd, and the
+ * file re-use cannot happen.
+ *
+ * For the same reason we can avoid a rcu_read_lock() around the
+ * operation - 'ffd.file' cannot go away even if the refcount has
+ * reached zero (but we must still not call out to ->poll() functions
+ * etc).
+ */
+static struct file *epi_fget(const struct epitem *epi)
+{
+ struct file *file;
+
+ file = epi->ffd.file;
+ if (!atomic_long_inc_not_zero(&file->f_count))
+ file = NULL;
+ return file;
+}
+
/*
* Called with &file->f_lock held,
* returns with it released
@@ -886,34 +914,6 @@ static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int dep
return res;
}
-/*
- * The ffd.file pointer may be in the process of being torn down due to
- * being closed, but we may not have finished eventpoll_release() yet.
- *
- * Normally, even with the atomic_long_inc_not_zero, the file may have
- * been free'd and then gotten re-allocated to something else (since
- * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU).
- *
- * But for epoll, users hold the ep->mtx mutex, and as such any file in
- * the process of being free'd will block in eventpoll_release_file()
- * and thus the underlying file allocation will not be free'd, and the
- * file re-use cannot happen.
- *
- * For the same reason we can avoid a rcu_read_lock() around the
- * operation - 'ffd.file' cannot go away even if the refcount has
- * reached zero (but we must still not call out to ->poll() functions
- * etc).
- */
-static struct file *epi_fget(const struct epitem *epi)
-{
- struct file *file;
-
- file = epi->ffd.file;
- if (!atomic_long_inc_not_zero(&file->f_count))
- file = NULL;
- return file;
-}
-
/*
* Differs from ep_eventpoll_poll() in that internal callers already have
* the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* [PATCH 6.1.y 9/9] eventpoll: fix ep_remove struct eventpoll / struct file UAF
2026-06-28 14:20 ` Salvatore Bonaccorso
` (8 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 8/9] eventpoll: move epi_fget() up Wentao Guan
@ 2026-06-28 16:19 ` Wentao Guan
2026-06-28 16:34 ` [PATCH 6.6.y 0/8] " Wentao Guan
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:19 UTC (permalink / raw)
To: carnil
Cc: benh, brauner, foss+kernel, gregkh, guanwentao, sashal, stable,
Jaeyoung Chung
From: Christian Brauner <brauner@kernel.org>
[ Upstream commit a6dc643c69311677c574a0f17a3f4d66a5f3744b ]
ep_remove() (via ep_remove_file()) cleared file->f_ep under
file->f_lock but then kept using @file inside the critical section
(is_file_epoll(), hlist_del_rcu() through the head, spin_unlock).
A concurrent __fput() taking the eventpoll_release() fastpath in
that window observed the transient NULL, skipped
eventpoll_release_file() and ran to f_op->release / file_free().
For the epoll-watches-epoll case, f_op->release is
ep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), which
kfree()s the watched struct eventpoll. Its embedded ->refs
hlist_head is exactly where epi->fllink.pprev points, so the
subsequent hlist_del_rcu()'s "*pprev = next" scribbles into freed
kmalloc-192 memory.
In addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot
backing @file could be recycled by alloc_empty_file() --
reinitializing f_lock and f_ep -- while ep_remove() is still
nominally inside that lock. The upshot is an attacker-controllable
kmem_cache_free() against the wrong slab cache.
Pin @file via epi_fget() at the top of ep_remove() and gate the
critical section on the pin succeeding. With the pin held @file
cannot reach refcount zero, which holds __fput() off and
transitively keeps the watched struct eventpoll alive across the
hlist_del_rcu() and the f_lock use, closing both UAFs.
If the pin fails @file has already reached refcount zero and its
__fput() is in flight. Because we bailed before clearing f_ep,
that path takes the eventpoll_release() slow path into
eventpoll_release_file() and blocks on ep->mtx until the waiter
side's ep_clear_and_put() drops it. The bailed epi's share of
ep->refcount stays intact, so the trailing ep_refcount_dec_and_test()
in ep_clear_and_put() cannot free the eventpoll out from under
eventpoll_release_file(); the orphaned epi is then cleaned up
there.
A successful pin also proves we are not racing
eventpoll_release_file() on this epi, so drop the now-redundant
re-check of epi->dying under f_lock. The cheap lockless
READ_ONCE(epi->dying) fast-path bailout stays.
Fixes: 58c9b016e128 ("epoll: use refcount to reduce ep_mutex contention")
Reported-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-6-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
(cherry picked from commit a6dc643c69311677c574a0f17a3f4d66a5f3744b)
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
fs/eventpoll.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 67ba8bf17b800..799fdf442e433 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -801,22 +801,26 @@ static bool ep_remove_epi(struct eventpoll *ep, struct epitem *epi)
*/
static void ep_remove(struct eventpoll *ep, struct epitem *epi)
{
- struct file *file = epi->ffd.file;
+ struct file *file __free(fput) = NULL;
lockdep_assert_irqs_enabled();
lockdep_assert_held(&ep->mtx);
ep_unregister_pollwait(ep, epi);
- /* sync with eventpoll_release_file() */
+ /* cheap sync with eventpoll_release_file() */
if (unlikely(READ_ONCE(epi->dying)))
return;
- spin_lock(&file->f_lock);
- if (epi->dying) {
- spin_unlock(&file->f_lock);
+ /*
+ * If we manage to grab a reference it means we're not in
+ * eventpoll_release_file() and aren't going to be.
+ */
+ file = epi_fget(epi);
+ if (!file)
return;
- }
+
+ spin_lock(&file->f_lock);
ep_remove_file(ep, epi, file);
if (ep_remove_epi(ep, epi))
--
2.30.2
^ permalink raw reply related [flat|nested] 22+ messages in thread* Re: [PATCH 6.6.y 0/8] eventpoll: fix ep_remove struct eventpoll / struct file UAF
2026-06-28 14:20 ` Salvatore Bonaccorso
` (9 preceding siblings ...)
2026-06-28 16:19 ` [PATCH 6.1.y 9/9] eventpoll: fix ep_remove struct eventpoll / struct file UAF Wentao Guan
@ 2026-06-28 16:34 ` Wentao Guan
10 siblings, 0 replies; 22+ messages in thread
From: Wentao Guan @ 2026-06-28 16:34 UTC (permalink / raw)
To: carnil, sashal; +Cc: benh, brauner, foss+kernel, gregkh, guanwentao, stable
Hello,
> On Fri, Jun 26, 2026 at 01:54:18PM -0400, Sasha Levin wrote:
> > > [PATCH 6.6.y 0/8] eventpoll: fix ep_remove struct eventpoll /
> > > struct file UAF (CVE-2026-46242)
> >
> > Whole series queued for 6.6, thanks.
>
> 58c9b016e128 ("epoll: use refcount to reduce ep_mutex contention") got
> backported as well to v6.1.175 and v5.15.209, will you provide
> backports for the 6.1.y and 5.15.y series as well?
You can try it for 6.1.y, it also clean apply and build successfuly for 5.15.y:
https://lore.kernel.org/stable/20260628161933.532572-1-guanwentao@uniontech.com/
please give a review.
BRs
Wentao Guan
^ permalink raw reply [flat|nested] 22+ messages in thread