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Subject[PATCH] uprobes: mmap_region() corrupts mm->mm_rb if uprobe_mmap() fails
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).

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.

Change mmap_region() and dup_mmap() to ignore the error code from
uprobe_mmap().

Reported-by: William Cohen <wcohen@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org> # v3.5
---
kernel/fork.c | 4 ++--
mm/mmap.c | 5 ++---
2 files changed, 4 insertions(+), 5 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index ab5211b..54bb88a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -454,8 +454,8 @@ 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 4fe2697..f25fd3f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1355,9 +1355,8 @@ 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;

--
1.5.5.1



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