From: Jay Lang jaytlang@mit.edu
commit 4bfe6cce133cad82cea04490c308795275857782 upstream.
In the copy_process() routine called by _do_fork(), failure to allocate a PID (or further along in the function) will trigger an invocation to exit_thread(). This is done to clean up from an earlier call to copy_thread_tls(). Naturally, the child task is passed into exit_thread(), however during the process, io_bitmap_exit() nullifies the parent's io_bitmap rather than the child's.
As copy_thread_tls() has been called ahead of the failure, the reference count on the calling thread's io_bitmap is incremented as we would expect. However, io_bitmap_exit() doesn't accept any arguments, and thus assumes it should trash the current thread's io_bitmap reference rather than the child's. This is pretty sneaky in practice, because in all instances but this one, exit_thread() is called with respect to the current task and everything works out.
A determined attacker can issue an appropriate ioctl (i.e. KDENABIO) to get a bitmap allocated, and force a clone3() syscall to fail by passing in a zeroed clone_args structure. The kernel handles the erroneous struct and the buggy code path is followed, and even though the parent's reference to the io_bitmap is trashed, the child still holds a reference and thus the structure will never be freed.
Fix this by tweaking io_bitmap_exit() and its subroutines to accept a task_struct argument which to operate on.
Fixes: ea5f1cd7ab49 ("x86/ioperm: Remove bitmap if all permissions dropped") Signed-off-by: Jay Lang jaytlang@mit.edu Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable#@vger.kernel.org Link: https://lkml.kernel.org/r/20200524162742.253727-1-jaytlang@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/io_bitmap.h | 4 ++-- arch/x86/kernel/ioport.c | 22 +++++++++++----------- arch/x86/kernel/process.c | 4 ++-- 3 files changed, 15 insertions(+), 15 deletions(-)
--- a/arch/x86/include/asm/io_bitmap.h +++ b/arch/x86/include/asm/io_bitmap.h @@ -17,7 +17,7 @@ struct task_struct;
#ifdef CONFIG_X86_IOPL_IOPERM void io_bitmap_share(struct task_struct *tsk); -void io_bitmap_exit(void); +void io_bitmap_exit(struct task_struct *tsk);
void native_tss_update_io_bitmap(void);
@@ -29,7 +29,7 @@ void native_tss_update_io_bitmap(void);
#else static inline void io_bitmap_share(struct task_struct *tsk) { } -static inline void io_bitmap_exit(void) { } +static inline void io_bitmap_exit(struct task_struct *tsk) { } static inline void tss_update_io_bitmap(void) { } #endif
--- a/arch/x86/kernel/ioport.c +++ b/arch/x86/kernel/ioport.c @@ -32,15 +32,15 @@ void io_bitmap_share(struct task_struct set_tsk_thread_flag(tsk, TIF_IO_BITMAP); }
-static void task_update_io_bitmap(void) +static void task_update_io_bitmap(struct task_struct *tsk) { - struct thread_struct *t = ¤t->thread; + struct thread_struct *t = &tsk->thread;
if (t->iopl_emul == 3 || t->io_bitmap) { /* TSS update is handled on exit to user space */ - set_thread_flag(TIF_IO_BITMAP); + set_tsk_thread_flag(tsk, TIF_IO_BITMAP); } else { - clear_thread_flag(TIF_IO_BITMAP); + clear_tsk_thread_flag(tsk, TIF_IO_BITMAP); /* Invalidate TSS */ preempt_disable(); tss_update_io_bitmap(); @@ -48,12 +48,12 @@ static void task_update_io_bitmap(void) } }
-void io_bitmap_exit(void) +void io_bitmap_exit(struct task_struct *tsk) { - struct io_bitmap *iobm = current->thread.io_bitmap; + struct io_bitmap *iobm = tsk->thread.io_bitmap;
- current->thread.io_bitmap = NULL; - task_update_io_bitmap(); + tsk->thread.io_bitmap = NULL; + task_update_io_bitmap(tsk); if (iobm && refcount_dec_and_test(&iobm->refcnt)) kfree(iobm); } @@ -101,7 +101,7 @@ long ksys_ioperm(unsigned long from, uns if (!iobm) return -ENOMEM; refcount_set(&iobm->refcnt, 1); - io_bitmap_exit(); + io_bitmap_exit(current); }
/* @@ -133,7 +133,7 @@ long ksys_ioperm(unsigned long from, uns } /* All permissions dropped? */ if (max_long == UINT_MAX) { - io_bitmap_exit(); + io_bitmap_exit(current); return 0; }
@@ -191,7 +191,7 @@ SYSCALL_DEFINE1(iopl, unsigned int, leve }
t->iopl_emul = level; - task_update_io_bitmap(); + task_update_io_bitmap(current);
return 0; } --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -97,7 +97,7 @@ int arch_dup_task_struct(struct task_str }
/* - * Free current thread data structures etc.. + * Free thread data structures etc.. */ void exit_thread(struct task_struct *tsk) { @@ -105,7 +105,7 @@ void exit_thread(struct task_struct *tsk struct fpu *fpu = &t->fpu;
if (test_thread_flag(TIF_IO_BITMAP)) - io_bitmap_exit(); + io_bitmap_exit(tsk);
free_vm86(t);