uprobes: Fix mmap_region()'s mm->mm_rb corruption if uprobe_mmap() fails

This patch fixes:

  https://bugzilla.redhat.com/show_bug.cgi?id=843640

If mmap_region()->uprobe_mmap() fails, unmap_and_free_vma path
does unmap_region() but does not remove the soon-to-be-freed vma
from rb tree. Actually there are more problems but this is how
William noticed this bug.

Perhaps we could do do_munmap() + return in this case, but in
fact it is simply wrong to abort if uprobe_mmap() fails. Until
at least we move the !UPROBE_COPY_INSN code from
install_breakpoint() to uprobe_register().

For example, uprobe_mmap()->install_breakpoint() can fail if the
probed insn is not supported (remember, uprobe_register()
succeeds if nobody mmaps inode/offset), mmap() should not fail
in this case.

dup_mmap()->uprobe_mmap() is wrong too by the same reason,
fork() can race with uprobe_register() and fail for no reason if
it wins the race and does install_breakpoint() first.

And, if nothing else, both mmap_region() and dup_mmap() return
success if uprobe_mmap() fails. Change them to ignore the error
code from uprobe_mmap().

Reported-and-tested-by: William Cohen <wcohen@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org> # v3.5
Cc: Anton Arapov <anton@redhat.com>
Cc: William Cohen <wcohen@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120819171042.GB26957@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 4 insertions, 5 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 3bd2280d79f6..2c8857e12855 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -455,8 +455,8 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
                 if (retval)
                         goto out;
 
-                if (file && uprobe_mmap(tmp))
-                        goto out;
+                if (file)
+                        uprobe_mmap(tmp);
         }
         /* a new mm has just been created */
         arch_dup_mmap(oldmm, mm);
diff --git a/mm/mmap.c b/mm/mmap.c
index e3e86914f11a..52e08fc9186d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1356,9 +1356,8 @@ out:
         } else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
                 make_pages_present(addr, addr + len);
 
-        if (file && uprobe_mmap(vma))
-                /* matching probes but cannot insert */
-                goto unmap_and_free_vma;
+        if (file)
+                uprobe_mmap(vma);
 
         return addr;