Commit 51246bfd189064079c54421507236fd2723b18f3
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futex: Handle user space corruption gracefully
If the owner of a PI futex dies we fix up the pi_state and set pi_state->owner to NULL. When a malicious or just sloppy programmed user space application sets the futex value to 0 e.g. by calling pthread_mutex_init(), then the futex can be acquired again. A new waiter manages to enqueue itself on the pi_state w/o damage, but on unlock the kernel dereferences pi_state->owner and oopses. Prevent this by checking pi_state->owner in the unlock path. If pi_state->owner is not current we know that user space manipulated the futex value. Ignore the mess and return -EINVAL. This catches the above case and also the case where a task hijacks the futex by setting the tid value and then tries to unlock it. Reported-by: Jermome Marchand <jmarchan@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Darren Hart <dvhltc@us.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <stable@kernel.org>
Showing 1 changed file with 7 additions and 0 deletions Side-by-side Diff
kernel/futex.c
| ... | ... | @@ -758,6 +758,13 @@ |
| 758 | 758 | if (!pi_state) |
| 759 | 759 | return -EINVAL; |
| 760 | 760 | |
| 761 | + /* | |
| 762 | + * If current does not own the pi_state then the futex is | |
| 763 | + * inconsistent and user space fiddled with the futex value. | |
| 764 | + */ | |
| 765 | + if (pi_state->owner != current) | |
| 766 | + return -EINVAL; | |
| 767 | + | |
| 761 | 768 | raw_spin_lock(&pi_state->pi_mutex.wait_lock); |
| 762 | 769 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); |
| 763 | 770 |