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authorBrian Foster <bfoster@redhat.com>2022-08-16 17:54:07 +0200
committerVasily Gorbik <gor@linux.ibm.com>2022-08-25 15:12:32 +0200
commit13cccafe0edcd03bf1c841de8ab8a1c8e34f77d9 (patch)
treea420b52dafd1f45cb9d7647679fc1a48b5e793d4 /arch/s390
parentLinux 6.0-rc2 (diff)
downloadlinux-13cccafe0edcd03bf1c841de8ab8a1c8e34f77d9.tar.xz
linux-13cccafe0edcd03bf1c841de8ab8a1c8e34f77d9.zip
s390: fix double free of GS and RI CBs on fork() failure
The pointers for guarded storage and runtime instrumentation control blocks are stored in the thread_struct of the associated task. These pointers are initially copied on fork() via arch_dup_task_struct() and then cleared via copy_thread() before fork() returns. If fork() happens to fail after the initial task dup and before copy_thread(), the newly allocated task and associated thread_struct memory are freed via free_task() -> arch_release_task_struct(). This results in a double free of the guarded storage and runtime info structs because the fields in the failed task still refer to memory associated with the source task. This problem can manifest as a BUG_ON() in set_freepointer() (with CONFIG_SLAB_FREELIST_HARDENED enabled) or KASAN splat (if enabled) when running trinity syscall fuzz tests on s390x. To avoid this problem, clear the associated pointer fields in arch_dup_task_struct() immediately after the new task is copied. Note that the RI flag is still cleared in copy_thread() because it resides in thread stack memory and that is where stack info is copied. Signed-off-by: Brian Foster <bfoster@redhat.com> Fixes: 8d9047f8b967c ("s390/runtime instrumentation: simplify task exit handling") Fixes: 7b83c6297d2fc ("s390/guarded storage: simplify task exit handling") Cc: <stable@vger.kernel.org> # 4.15 Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Link: https://lore.kernel.org/r/20220816155407.537372-1-bfoster@redhat.com Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390')
-rw-r--r--arch/s390/kernel/process.c22
1 files changed, 16 insertions, 6 deletions
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 89949b9f3cf8..d5119e039d85 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -91,6 +91,18 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
memcpy(dst, src, arch_task_struct_size);
dst->thread.fpu.regs = dst->thread.fpu.fprs;
+
+ /*
+ * Don't transfer over the runtime instrumentation or the guarded
+ * storage control block pointers. These fields are cleared here instead
+ * of in copy_thread() to avoid premature freeing of associated memory
+ * on fork() failure. Wait to clear the RI flag because ->stack still
+ * refers to the source thread.
+ */
+ dst->thread.ri_cb = NULL;
+ dst->thread.gs_cb = NULL;
+ dst->thread.gs_bc_cb = NULL;
+
return 0;
}
@@ -150,13 +162,11 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
frame->childregs.flags = 0;
if (new_stackp)
frame->childregs.gprs[15] = new_stackp;
-
- /* Don't copy runtime instrumentation info */
- p->thread.ri_cb = NULL;
+ /*
+ * Clear the runtime instrumentation flag after the above childregs
+ * copy. The CB pointer was already cleared in arch_dup_task_struct().
+ */
frame->childregs.psw.mask &= ~PSW_MASK_RI;
- /* Don't copy guarded storage control block */
- p->thread.gs_cb = NULL;
- p->thread.gs_bc_cb = NULL;
/* Set a new TLS ? */
if (clone_flags & CLONE_SETTLS) {