write_opcode()->get_user_pages() needs FOLL_FORCE to ensure we can
read the page even if the probed task did mprotect(PROT_NONE) after
uprobe_register(). Without FOLL_WRITE, FOLL_FORCE doesn't have any
side effect but allows to read the !VM_READ memory.
Otherwiese the subsequent uprobe_unregister()->set_orig_insn() fails
and we leak "int3". If that task does mprotect(PROT_READ | EXEC) and
execute the probed insn later it will be killed.
Note: in fact this is also needed for _register, see the next patch.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/events/uprobes.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 14c2e99..fa1579a 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -221,7 +221,7 @@ static int write_opcode(struct arch_uprobe *auprobe, struct
mm_struct *mm,
retry:
/* Read the page with vaddr into memory */
- ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &old_page, &vma);
+ ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma);
if (ret <= 0)
return ret;
--
1.5.5.1
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