From: Linus Torvalds <torvalds@linux-foundation.org> mainline inclusion from mainline-v7.1-rc4 commit 31e62c2ebbfdc3fe3dbdf5e02c92a9dc67087a3a category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15055 CVE: CVE-2026-46333 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- The 'dumpability' of a task is fundamentally about the memory image of the task - the concept comes from whether it can core dump or not - and makes no sense when you don't have an associated mm. And almost all users do in fact use it only for the case where the task has a mm pointer. But we have one odd special case: ptrace_may_access() uses 'dumpable' to check various other things entirely independently of the MM (typically explicitly using flags like PTRACE_MODE_READ_FSCREDS). Including for threads that no longer have a VM (and maybe never did, like most kernel threads). It's not what this flag was designed for, but it is what it is. The ptrace code does check that the uid/gid matches, so you do have to be uid-0 to see kernel thread details, but this means that the traditional "drop capabilities" model doesn't make any difference for this all. Make it all make a *bit* more sense by saying that if you don't have a MM pointer, we'll use a cached "last dumpability" flag if the thread ever had a MM (it will be zero for kernel threads since it is never set), and require a proper CAP_SYS_PTRACE capability to override. Reported-by: Qualys Security Advisory <qsa@qualys.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Kees Cook <kees@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Conflicts: include/linux/sched.h kernel/exit.c kernel/ptrace.c [ctx conflicts] Signed-off-by: Pu Lehui <pulehui@huawei.com> --- include/linux/sched.h | 3 +++ kernel/exit.c | 1 + kernel/ptrace.c | 22 ++++++++++++++++------ 3 files changed, 20 insertions(+), 6 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 608100b3cf3d..9fbe6b7fd3bf 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -763,6 +763,9 @@ struct task_struct { /* Unserialized, strictly 'current' */ + /* Save user-dumpable when mm goes away */ + unsigned user_dumpable:1; + /* Bit to tell LSMs we're in execve(): */ unsigned in_execve:1; unsigned in_iowait:1; diff --git a/kernel/exit.c b/kernel/exit.c index 358a635743ac..cfaa2df2bffc 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -470,6 +470,7 @@ static void exit_mm(void) BUG_ON(mm != current->active_mm); /* more a memory barrier than a real lock */ task_lock(current); + current->user_dumpable = (get_dumpable(mm) == SUID_DUMP_USER); current->mm = NULL; up_read(&mm->mmap_sem); enter_lazy_tlb(mm, current); diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 424a04cdda1d..4e4a0d34085b 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -282,11 +282,24 @@ static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode) return has_ns_capability(current, ns, CAP_SYS_PTRACE); } +static bool task_still_dumpable(struct task_struct *task, unsigned int mode) +{ + struct mm_struct *mm = task->mm; + if (mm) { + if (get_dumpable(mm) == SUID_DUMP_USER) + return true; + return ptrace_has_cap(mm->user_ns, mode); + } + + if (task->user_dumpable) + return true; + return ptrace_has_cap(&init_user_ns, mode); +} + /* Returns 0 on success, -errno on denial. */ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) { const struct cred *cred = current_cred(), *tcred; - struct mm_struct *mm; kuid_t caller_uid; kgid_t caller_gid; @@ -347,11 +360,8 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) * Pairs with a write barrier in commit_creds(). */ smp_rmb(); - mm = task->mm; - if (mm && - ((get_dumpable(mm) != SUID_DUMP_USER) && - !ptrace_has_cap(mm->user_ns, mode))) - return -EPERM; + if (!task_still_dumpable(task, mode)) + return -EPERM; return security_ptrace_access_check(task, mode); } -- 2.34.1