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s390/uaccess: test if current->mm is set before walking page tables

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If get_fs() == USER_DS we better test if current->mm is not zero before
walking page tables.
The page table walk code would try to lock mm->page_table_lock, however
if mm is zero this might crash.

Now it is arguably incorrect trying to access userspace if current->mm
is zero, however we have seen that and s390 would be the only architecture
which would crash in such a case.
So we better make the page table walk code a bit more robust and report
always a fault instead.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2014-01-17 13:12:34 +01:00 committed by Martin Schwidefsky
parent 05e9181bdb
commit b03b467944
1 changed files with 10 additions and 0 deletions
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10
arch/s390/lib/uaccess_pt.c
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@ -153,6 +153,8 @@ static __always_inline size_t __user_copy_pt(unsigned long uaddr, void *kptr,
unsigned long offset, done, size, kaddr;
void *from, *to;
if (!mm)
return n;
done = 0;
retry:
spin_lock(&mm->page_table_lock);
@ -262,6 +264,8 @@ static size_t strnlen_user_pt(size_t count, const char __user *src)
return 0;
if (segment_eq(get_fs(), KERNEL_DS))
return strnlen_kernel(count, src);
if (!mm)
return 0;
done = 0;
retry:
spin_lock(&mm->page_table_lock);
@ -323,6 +327,8 @@ static size_t copy_in_user_pt(size_t n, void __user *to,
if (segment_eq(get_fs(), KERNEL_DS))
return copy_in_kernel(n, to, from);
if (!mm)
return n;
done = 0;
retry:
spin_lock(&mm->page_table_lock);
@ -411,6 +417,8 @@ int futex_atomic_op_pt(int op, u32 __user *uaddr, int oparg, int *old)
if (segment_eq(get_fs(), KERNEL_DS))
return __futex_atomic_op_pt(op, uaddr, oparg, old);
if (unlikely(!current->mm))
return -EFAULT;
spin_lock(&current->mm->page_table_lock);
uaddr = (u32 __force __user *)
__dat_user_addr((__force unsigned long) uaddr, 1);
@ -448,6 +456,8 @@ int futex_atomic_cmpxchg_pt(u32 *uval, u32 __user *uaddr,
if (segment_eq(get_fs(), KERNEL_DS))
return __futex_atomic_cmpxchg_pt(uval, uaddr, oldval, newval);
if (unlikely(!current->mm))
return -EFAULT;
spin_lock(&current->mm->page_table_lock);
uaddr = (u32 __force __user *)
__dat_user_addr((__force unsigned long) uaddr, 1);