Merge pull request #1191 from dmbaturin/T8871-ptrace-vuln

Kernel: T8871: add a patch for the ptrace vulnerability that allows unprivileged users to read files owned by any other user

Author: dmbaturin

scripts/package-build/linux-kernel/patches/kernel/0005-ptrace-slightly-saner-get_dumpable-logic.patch

@@ -0,0 +1,110 @@
+From 31e62c2ebbfdc3fe3dbdf5e02c92a9dc67087a3a Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Wed, 13 May 2026 11:37:18 -0700
+Subject: [PATCH] ptrace: slightly saner 'get_dumpable()' logic
+
+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>
+---
+ 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 368c7b4d7cb510..ee06cba5c6f538 100644
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -1002,6 +1002,9 @@ struct task_struct {
+ 	unsigned			sched_rt_mutex:1;
+ #endif
+ 
++	/* Save user-dumpable when mm goes away */
++	unsigned			user_dumpable:1;
++
+ 	/* Bit to tell TOMOYO we're in execve(): */
+ 	unsigned			in_execve:1;
+ 	unsigned			in_iowait:1;
+diff --git a/kernel/exit.c b/kernel/exit.c
+index 9a909993ab1d8b..f50d73c272d6ee 100644
+--- a/kernel/exit.c
++++ b/kernel/exit.c
+@@ -571,6 +571,7 @@ static void exit_mm(void)
+ 	 */
+ 	smp_mb__after_spinlock();
+ 	local_irq_disable();
++	current->user_dumpable = (get_dumpable(mm) == SUID_DUMP_USER);
+ 	current->mm = NULL;
+ 	membarrier_update_current_mm(NULL);
+ 	enter_lazy_tlb(mm, current);
+diff --git a/kernel/ptrace.c b/kernel/ptrace.c
+index 68c17daef8d40b..130043bfc2091c 100644
+--- a/kernel/ptrace.c
++++ b/kernel/ptrace.c
+@@ -272,11 +272,24 @@ static bool ptrace_has_cap(struct user_namespace *ns, unsigned int mode)
+ 	return ns_capable(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;
+ 
+@@ -337,11 +350,8 @@ 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);
+ }