From: Max Kellermann <max.kellermann@ionos.com> stable inclusion from stable-v5.10.266 commit b5661524c5a45085a866864ca9b8ae2513dfd67a category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/18404 CVE: CVE-2026-80527 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 50958bb928bad3bdba9e5d1b7ff4bbadcf6951e6 ] A reader can hang forever in __ceph_get_caps() when the client no longer holds `FILE_RD`, but local cap state still says that the capability is already wanted (via `mds_wanted`). One way to trigger this is through MDS cap revocation. If another client performs a conflicting operation, the MDS can revoke `FILE_RD` from the reader; the next read then has to reacquire `FILE_RD`. If the cap update that should request `FILE_RD` never reaches the MDS after `cap->mds_wanted` was raised, the reader is left holding only non-file caps while local `mds_wanted` still includes the file read caps. In that state, try_get_cap_refs() sees `need <= mds_wanted` and returns 0, so __ceph_get_caps() just waits on `i_cap_wq`. If the cap update that was supposed to request `FILE_RD never reaches the MDS after `cap->mds_wanted was` raised, no further request is sent and the waiter can sleep indefinitely until unrelated cap traffic happens to wake it up. The ordering issue is that `cap->mds_wanted` is updated in __prep_cap() before the `CEPH_MSG_CLIENT_CAPS message` is actually queued for send. That makes one field serve two different meanings at once: what this client wants, and what the client believes the MDS already knows it wants. A proper fix would be to split those states and track whether a cap update is actually in flight or has been observed by the MDS. However, simply moving the `cap->mds_wanted assignment` later would not be sufficient: queueing the message in the messenger does not guarantee that the MDS processed that specific wanted set, and reconnect or message loss can still invalidate that assumption. Fixing that properly would require a larger rework of the cap state machine. To allow simpler backports to stable kernels, this patch implements a simpler workaround: - stop waiting forever in __ceph_get_caps(); after a bounded wait, fall back to the renew path - make ceph_renew_caps() issue a synchronous `OPEN` request whenever the inode still does not actually hold the wanted caps, instead of only calling ceph_check_caps() The extra issued-vs-wanted check in ceph_renew_caps() is necessary because the previous test only checked whether the inode still had any real caps at all. That is not enough after revocation: the client can still hold something like `pLs` and yet be missing `FILE_RD` completely. In that case, falling back to ceph_check_caps() is not sufficient, because it still trusts `cap->mds_wanted` and may resend nothing. By requiring `(issued & wanted) == wanted` before taking the asynchronous path, the code only uses ceph_check_caps() when the `wanted caps` are already actually issued. Otherwise, it sends the synchronous `OPEN` renew. This preserves the existing asynchronous fast path when the wanted caps are already issued, avoids changing cap-state semantics, and fixes the hang by guaranteeing that a stalled waiter eventually retries through a path that does not rely on the stale `mds_wanted` state. [ idryomov: move CEPH_GET_CAPS_WAIT_TIMEOUT from libceph.h to mds_client.h, formatting ] Cc: stable@vger.kernel.org Fixes: 0a454bdd501a ("ceph: reorganize __send_cap for less spinlock abuse") Signed-off-by: Max Kellermann <max.kellermann@ionos.com> Reviewed-by: Alex Markuze <amarkuze@redhat.com> Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Tengda Wu <wutengda2@huawei.com> --- fs/ceph/caps.c | 17 +++++++++++++++-- fs/ceph/file.c | 9 +++++---- fs/ceph/mds_client.h | 2 ++ 3 files changed, 22 insertions(+), 6 deletions(-) diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c index 31e5d87ec945..9bebdafd5ec9 100644 --- a/fs/ceph/caps.c +++ b/fs/ceph/caps.c @@ -2995,7 +2995,19 @@ int ceph_get_caps(struct file *filp, int need, int want, ret = -ERESTARTSYS; break; } - wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); + + /* + * If a cap update is lost after + * mds_wanted was raised, waiting + * forever will never make progress. + * Retry the renew path periodically + * so we can resend synchronously. + */ + if (!wait_woken(&wait, TASK_INTERRUPTIBLE, + CEPH_GET_CAPS_WAIT_TIMEOUT)) { + ret = -ESTALE; + break; + } } remove_wait_queue(&ci->i_cap_wq, &wait); @@ -3027,7 +3039,8 @@ int ceph_get_caps(struct file *filp, int need, int want, continue; } if (ret == -ESTALE) { - /* session was killed, try renew caps */ + /* session was killed or a waited cap + * request needs a retry */ ret = ceph_renew_caps(inode, flags); if (ret == 0) continue; diff --git a/fs/ceph/file.c b/fs/ceph/file.c index 215bd9a3c535..f20d5f708009 100644 --- a/fs/ceph/file.c +++ b/fs/ceph/file.c @@ -277,21 +277,22 @@ static int ceph_init_file(struct inode *inode, struct file *file, int fmode) } /* - * try renew caps after session gets killed. + * Retry cap acquisition after a stale session or a lost cap update. */ int ceph_renew_caps(struct inode *inode, int fmode) { struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(inode->i_sb); struct ceph_inode_info *ci = ceph_inode(inode); struct ceph_mds_request *req; - int err, flags, wanted; + int err, flags, wanted, issued; spin_lock(&ci->i_ceph_lock); __ceph_touch_fmode(ci, mdsc, fmode); wanted = __ceph_caps_file_wanted(ci); + issued = __ceph_caps_issued(ci, NULL); if (__ceph_is_any_real_caps(ci) && - (!(wanted & CEPH_CAP_ANY_WR) || ci->i_auth_cap)) { - int issued = __ceph_caps_issued(ci, NULL); + (!(wanted & CEPH_CAP_ANY_WR) || ci->i_auth_cap) && + (issued & wanted) == wanted) { spin_unlock(&ci->i_ceph_lock); dout("renew caps %p want %s issued %s updating mds_wanted\n", inode, ceph_cap_string(wanted), ceph_cap_string(issued)); diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h index 1c958510f00f..b1939f916228 100644 --- a/fs/ceph/mds_client.h +++ b/fs/ceph/mds_client.h @@ -61,6 +61,8 @@ enum ceph_feature_type { struct ceph_fs_client; struct ceph_cap; +#define CEPH_GET_CAPS_WAIT_TIMEOUT (5 * HZ) + /* * parsed info about a single inode. pointers are into the encoded * on-wire structures within the mds reply message payload. -- 2.34.1