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Fix CVE-2026-46242 (eventpoll ep_remove UAF); bump to 687.20.3

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This commit is contained in:
Andrew Lukoshko 2026-07-06 12:57:07 +00:00
parent 5ff608da79
commit 0a570b6523
2 changed files with 107 additions and 2 deletions
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99
SOURCES/1712-eventpoll-fix-ep-remove-struct-eventpoll-struct-file-uaf.patch Normal file
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@ -0,0 +1,99 @@
From: Christian Brauner <brauner@kernel.org>
Date: Thu, 23 Apr 2026 11:56:09 +0200
Subject: [PATCH] eventpoll: fix ep_remove struct eventpoll / struct file UAF
CVE: CVE-2026-46242
Upstream commit a6dc643c69311677c574a0f17a3f4d66a5f3744b, adapted to the
pre-e9e5cd40d7c4 ("eventpoll: kill __ep_remove()") code shape still used
by this kernel, where the removal path is the monolithic __ep_remove(ep,
epi, force) rather than upstream's ep_remove()/ep_remove_epi()/
ep_remove_file() split.
ep_remove() used epi->ffd.file across the file->f_lock critical section
without holding a reference. A concurrent __fput() taking the
eventpoll_release() fastpath could free the file (and, for the
epoll-watches-epoll case, the watched struct eventpoll) mid-section,
leading to a use-after-free / attacker-controllable kmem_cache_free().
Pin the file with epi_fget() before entering the critical section and
release it afterwards. A failed pin means __fput() is already in flight
and will remove the epi via eventpoll_release_file() (which blocks on
ep->mtx), so it is safe to bail. The pin is taken only on the !force
path: the force path is reached from eventpoll_release_file() itself,
i.e. from within __fput() where f_count has already dropped to zero and
epi_fget() would necessarily fail; there @file is still valid and no
concurrent __fput() can race, so it keeps using epi->ffd.file directly.
A successful pin also makes the in-lock epi->dying recheck redundant; the
cheap lockless READ_ONCE(epi->dying) fast-path bailout is kept.
Fixes: 58c9b016e128 ("epoll: use refcount to reduce ep_mutex contention")
Reported-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 14e7663..9c56062 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -711,6 +711,8 @@ static void ep_free(struct eventpoll *ep)
kfree(ep);
}
+static struct file *epi_fget(const struct epitem *epi);
+
/*
* Removes a "struct epitem" from the eventpoll RB tree and deallocates
* all the associated resources. Must be called with "mtx" held.
@@ -722,6 +724,7 @@ 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 file *to_put = NULL;
struct epitems_head *to_free;
struct hlist_head *head;
@@ -732,13 +735,27 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
*/
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;
+ if (!force) {
+ /* cheap sync with eventpoll_release_file() */
+ if (unlikely(READ_ONCE(epi->dying)))
+ return false;
+ /*
+ * Grabbing a reference proves we are not racing
+ * eventpoll_release_file() and are not going to: a concurrent
+ * __fput() cannot free @file (nor, for the epoll-on-epoll
+ * case, the watched eventpoll) across the f_lock section
+ * below. A failed pin means @file already reached refcount
+ * zero and __fput() is in flight; it will remove this epi via
+ * eventpoll_release_file(), so bail out here.
+ */
+ file = epi_fget(epi);
+ if (!file)
+ return false;
+ to_put = file;
}
+ /* Remove the current item from the list of epoll hooks */
+ spin_lock(&file->f_lock);
to_free = NULL;
head = file->f_ep;
if (head->first == &epi->fllink && !epi->fllink.next) {
@@ -772,6 +789,8 @@ 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);
+ if (to_put)
+ fput(to_put);
return true;
}
--
2.43.0

10
SPECS/kernel.spec
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@ -176,13 +176,13 @@ Summary: The Linux kernel
# define buildid .local
%define specversion 5.14.0
%define patchversion 5.14
%define pkgrelease 687.20.1
%define pkgrelease 687.20.3
%define kversion 5
%define tarfile_release 5.14.0-687.5.1.el9_8
# This is needed to do merge window version magic
%define patchlevel 14
# This allows pkg_release to have configurable %%{?dist} tag
%define specrelease 687.20.2%{?buildid}%{?dist}
%define specrelease 687.20.3%{?buildid}%{?dist}
# This defines the kabi tarball version
%define kabiversion 5.14.0-687.5.1.el9_8
@ -1589,6 +1589,7 @@ Patch1708: 1708-crypto-krb5enc-fix-async-decrypt-skipping-hash-verification.patc
Patch1709: 1709-crypto-krb5-filter-out-async-aead-implementations-at-alloc.patch
Patch1710: 1710-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-gfn.patch
Patch1711: 1711-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-role.patch
Patch1712: 1712-eventpoll-fix-ep-remove-struct-eventpoll-struct-file-uaf.patch
# END OF PATCH DEFINITIONS
%description
@ -2945,6 +2946,7 @@ ApplyPatch 1708-crypto-krb5enc-fix-async-decrypt-skipping-hash-verification.patc
ApplyPatch 1709-crypto-krb5-filter-out-async-aead-implementations-at-alloc.patch
ApplyPatch 1710-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-gfn.patch
ApplyPatch 1711-kvm-x86-fix-shadow-paging-use-after-free-due-to-unexpected-role.patch
ApplyPatch 1712-eventpoll-fix-ep-remove-struct-eventpoll-struct-file-uaf.patch
# END OF PATCH APPLICATIONS
# Any further pre-build tree manipulations happen here.
@ -5019,6 +5021,10 @@ fi
#
#
%changelog
* Mon Jul 06 2026 Andrew Lukoshko <alukoshko@almalinux.org> - 5.14.0-687.20.3
- Fix CVE-2026-46242: eventpoll ep_remove struct eventpoll / struct file
use-after-free, adapted from upstream a6dc643c6931 ahead of RHEL (1712)
* Thu Jul 02 2026 Andrew Lukoshko <alukoshko@almalinux.org> - 5.14.0-687.20.2
- Fix KVM x86 shadow paging use-after-free due to unexpected GFN ahead of RHEL (1710)
- Fix KVM x86 shadow paging use-after-free due to unexpected role ahead of RHEL (1711)