uprobes: Change write_opcode() to use FOLL_FORCE

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 <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 198d732ab9012e3802008e60d46a87065a003d7b..80e8c7b697b9fdd014daae4775ae6991fde353c4 100644 (file)
--- 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;