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4bfe6cce13
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: ea5f1cd7ab ("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
37 lines
850 B
C
37 lines
850 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_IOBITMAP_H
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#define _ASM_X86_IOBITMAP_H
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#include <linux/refcount.h>
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#include <asm/processor.h>
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struct io_bitmap {
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u64 sequence;
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refcount_t refcnt;
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/* The maximum number of bytes to copy so all zero bits are covered */
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unsigned int max;
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unsigned long bitmap[IO_BITMAP_LONGS];
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};
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struct task_struct;
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#ifdef CONFIG_X86_IOPL_IOPERM
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void io_bitmap_share(struct task_struct *tsk);
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void io_bitmap_exit(struct task_struct *tsk);
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void native_tss_update_io_bitmap(void);
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#ifdef CONFIG_PARAVIRT_XXL
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#include <asm/paravirt.h>
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#else
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#define tss_update_io_bitmap native_tss_update_io_bitmap
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#endif
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#else
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static inline void io_bitmap_share(struct task_struct *tsk) { }
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static inline void io_bitmap_exit(struct task_struct *tsk) { }
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static inline void tss_update_io_bitmap(void) { }
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#endif
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#endif
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