uprobes: __copy_insn() should ensure a_ops->readpage != NULL

__copy_insn() blindly calls read_mapping_page(), this will crash
the kernel if ->readpage == NULL, add the necessary check. For
example, hugetlbfs_aops->readpage is NULL. Perhaps we should
change read_mapping_page() instead.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120615154325.GA9568@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index f0d04530af63..604930bf9c92 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -610,6 +610,9 @@ __copy_insn(struct address_space *mapping, struct vm_area_struct *vma, char *ins
         if (!filp)
                 return -EINVAL;
 
+        if (!mapping->a_ops->readpage)
+                return -EIO;
+
         idx = (unsigned long)(offset >> PAGE_CACHE_SHIFT);
         off1 = offset &= ~PAGE_MASK;