From: Linpu Yu <linpu5433@gmail.com> stable inclusion from stable-v6.6.143 commit 157ce2c6836ce0ff19108a819f38df061345425f category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15641 CVE: CVE-2026-52923 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit fa0b9b2b7ae3539908d69c2b9ac0d144d9bc5139 upstream. The checkpoint/restore sysctl path can request the next SysV IPC id through ids->next_id. ipc_idr_alloc() currently forwards that request to idr_alloc() with an open-ended upper bound. If the valid tail of the SysV IPC id space is full, the allocation can spill beyond ipc_mni. The returned SysV IPC id still uses the normal index encoding, so later lookup and removal can target the wrong slot. This leaves the real IDR entry behind and breaks the IDR state for the object. The bug is in ipc_idr_alloc() in the checkpoint/restore path. 1. ids->next_id is passed to: idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id), 0, ...) 2. The zero upper bound makes the allocation effectively open-ended. Once the valid SysV IPC tail is occupied, idr_alloc() can spill past ipc_mni and allocate an entry beyond the valid IPC id range. 3. The new object id is still encoded with the narrower SysV IPC index width: new->id = (new->seq << ipcmni_seq_shift()) + idx 4. Later removal goes through ipc_rmid(), which uses: ipcid_to_idx(ipcp->id) That truncates the real IDR index. An object actually stored at a high index can then be removed as if it lived at a low in-range index. 5. For shared memory, shm_destroy() frees the current object anyway, but the real high IDR slot is left behind as a dangling pointer. 6. A subsequent walk of /proc/sysvipc/shm reaches the stale IDR entry and dereferences freed memory. Prevent this by bounding the requested allocation to ipc_mni so the checkpoint/restore path fails once the valid range is exhausted. Link: https://lore.kernel.org/cover.1778336914.git.linpu5433@gmail.com Link: https://lore.kernel.org/2eebe949bfa7d1f6e13b5be6a92c64c850ce9d45.1778336914.... Fixes: 03f595668017 ("ipc: add sysctl to specify desired next object id") Signed-off-by: Linpu Yu <linpu5433@gmail.com> Signed-off-by: Ren Wei <n05ec@lzu.edu.cn> Reported-by: Yuan Tan <yuantan098@gmail.com> Reported-by: Yifan Wu <yifanwucs@gmail.com> Reported-by: Juefei Pu <tomapufckgml@gmail.com> Reported-by: Xin Liu <bird@lzu.edu.cn> Cc: Kees Cook <kees@kernel.org> Cc: Stanislav Kinsbursky <skinsbursky@parallels.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Fanhua Li <lifanhua5@huawei.com> --- ipc/util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/ipc/util.c b/ipc/util.c index 05cb9de667350..14dec7e9c887c 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -253,7 +253,7 @@ static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new) } else { new->seq = ipcid_to_seqx(next_id); idx = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id), - 0, GFP_NOWAIT); + ipc_mni, GFP_NOWAIT); } if (idx >= 0) new->id = (new->seq << ipcmni_seq_shift()) + idx; -- 2.43.0