[PATCH OLK-6.6 0/6] Fix CVE-2026-46242
Fix CVE-2026-46242 Christian Brauner (6): 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: move epi_fget() up eventpoll: fix ep_remove struct eventpoll / struct file UAF fs/eventpoll.c | 128 ++++++++++++++++++++++++++++--------------------- 1 file changed, 73 insertions(+), 55 deletions(-) -- 2.52.0
From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.18.33 commit 9348f4763aa9b9e97fb006edc7aabd2aa209e5eb category: cleanup bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15497 CVE: CVE-2026-46242 Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/... -------------------------------- [ 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.or... 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: Sasha Levin <sashal@kernel.org> Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- fs/eventpoll.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 8a556560a5b2..4f05d12a0503 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -743,11 +743,11 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force) return false; } 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)) { struct epitems_head *v; v = container_of(head, struct epitems_head, epitems); -- 2.52.0
From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.18.33 commit 416b491cd2890470624a85d90ca53242f1ea68ef category: other bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15497 CVE: CVE-2026-46242 Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/... -------------------------------- [ 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.or... 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: Sasha Levin <sashal@kernel.org> Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- fs/eventpoll.c | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 4f05d12a0503..ae9cb8276448 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -713,10 +713,13 @@ static void ep_free(struct eventpoll *ep) wakeup_source_unregister(ep->ws); /* ep_get_upwards_depth_proc() may still hold epi->ep under RCU */ 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 @@ -724,12 +727,10 @@ static void ep_free(struct eventpoll *ep) * 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; - struct epitems_head *to_free; - struct hlist_head *head; lockdep_assert_irqs_enabled(); /* * Removes poll wait queue hooks. @@ -741,12 +742,25 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force) if (epi->dying && !force) { spin_unlock(&file->f_lock); 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); if (!is_file_epoll(file)) { struct epitems_head *v; @@ -756,10 +770,15 @@ 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); spin_lock_irq(&ep->lock); if (ep_is_linked(epi)) -- 2.52.0
From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.18.33 commit e084713397a415afa4166994d5af5afea20c2ef4 category: other bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15497 CVE: CVE-2026-46242 Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/... -------------------------------- [ 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.or... 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: Sasha Levin <sashal@kernel.org> Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- fs/eventpoll.c | 67 ++++++++++++++++++++++---------------------------- 1 file changed, 30 insertions(+), 37 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index ae9cb8276448..766716c2fd92 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -713,53 +713,22 @@ static void ep_free(struct eventpoll *ep) wakeup_source_unregister(ep->ws); /* ep_get_upwards_depth_proc() may still hold epi->ep under RCU */ 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. */ WRITE_ONCE(file->f_ep, NULL); if (!is_file_epoll(file)) { @@ -802,11 +771,29 @@ 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) { - 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)); } static void ep_clear_and_put(struct eventpoll *ep) { @@ -1011,20 +998,26 @@ void eventpoll_release_file(struct file *file) */ again: 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); /* * ep access is safe as we still own a reference to the ep * struct */ 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)) ep_free(ep); goto again; -- 2.52.0
From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.18.33 commit e644f892e1f27b7ed21a513a62b42dc1ca62d468 category: cleanup bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15497 CVE: CVE-2026-46242 Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/... -------------------------------- [ 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: Sasha Levin <sashal@kernel.org> Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- fs/eventpoll.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 766716c2fd92..0a54a4226357 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -717,11 +717,11 @@ 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; struct hlist_head *head = file->f_ep; @@ -741,11 +741,11 @@ static void __ep_remove_file(struct eventpoll *ep, struct epitem *epi, 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) +static bool ep_remove_epi(struct eventpoll *ep, struct epitem *epi) { lockdep_assert_held(&ep->mtx); rb_erase_cached(&epi->rbn, &ep->rbr); @@ -787,13 +787,13 @@ static void ep_remove_safe(struct eventpoll *ep, struct epitem *epi) spin_lock(&file->f_lock); if (epi->dying) { 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)); } static void ep_clear_and_put(struct eventpoll *ep) { @@ -1011,12 +1011,12 @@ void eventpoll_release_file(struct file *file) mutex_lock(&ep->mtx); 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); if (dispose && ep_refcount_dec_and_test(ep)) ep_free(ep); -- 2.52.0
From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.18.33 commit eb206b8f55e14985eb531e76cc741e0de6270df1 category: other bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15497 CVE: CVE-2026-46242 Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/... -------------------------------- [ 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.or... 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: Sasha Levin <sashal@kernel.org> Conflicts: fs/eventpoll.c [Simple context conflicts, not affect this patch.] Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- fs/eventpoll.c | 56 +++++++++++++++++++++++++------------------------- 1 file changed, 28 insertions(+), 28 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 0a54a4226357..ded92b40fba6 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -713,10 +713,38 @@ static void ep_free(struct eventpoll *ep) wakeup_source_unregister(ep->ws); /* ep_get_upwards_depth_proc() may still hold epi->ep under RCU */ 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 */ static void ep_remove_file(struct eventpoll *ep, struct epitem *epi, @@ -884,38 +912,10 @@ static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int dep ep_done_scan(ep, &txlist); mutex_unlock(&ep->mtx); 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() * is correctly annotated. */ -- 2.52.0
From: Christian Brauner <brauner@kernel.org> stable inclusion from stable-v6.18.33 commit ef4ca02e95363e78977ca04340d44fe3b4b2b81f category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15497 CVE: CVE-2026-46242 Reference: https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/... -------------------------------- [ 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.or... Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Conflicts: fs/eventpoll.c [Cleanup argument(fput) not a function on file. Call fput() manually.] Signed-off-by: Zizhi Wo <wozizhi@huawei.com> --- fs/eventpoll.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index ded92b40fba6..fa63e96020da 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -799,30 +799,36 @@ 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) { - struct file *file = epi->ffd.file; + struct file *file = 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)) WARN_ON_ONCE(ep_refcount_dec_and_test(ep)); + + fput(file); } static void ep_clear_and_put(struct eventpoll *ep) { struct rb_node *rbp, *next; -- 2.52.0
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