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    SubjectRe: [PATCH 1/5] kprobes: Do not use local variable when creating debugfs file
    On Wed,  9 Jun 2021 19:50:15 +0900
    Punit Agrawal <punitagrawal@gmail.com> wrote:

    > debugfs_create_file() takes a pointer argument that can be used during
    > file operation callbacks (accessible via i_private in the inode
    > structure). An obvious requirement is for the pointer to refer to
    > valid memory when used.
    >
    > When creating the debugfs file to dynamically enable / disable
    > kprobes, a pointer to local variable is passed to
    > debugfs_create_file(); which will go out of scope when the init
    > function returns. The reason this hasn't triggered random memory
    > corruption is because the pointer is not accessed during the debugfs
    > file callbacks.
    >
    > Fix the incorrect (and unnecessary) usage of local variable during
    > debugfs_file_create() by passing NULL instead.
    >

    Good catch! Since the enabled state is managed by the kprobes_all_disabled
    global variable, it is not needed.

    Fixes: bf8f6e5b3e51 ("Kprobes: The ON/OFF knob thru debugfs")
    Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

    Thank you!

    > Signed-off-by: Punit Agrawal <punitagrawal@gmail.com>
    > ---
    > kernel/kprobes.c | 3 +--
    > 1 file changed, 1 insertion(+), 2 deletions(-)
    >
    > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    > index 745f08fdd7a6..fdb1ea2e963b 100644
    > --- a/kernel/kprobes.c
    > +++ b/kernel/kprobes.c
    > @@ -2816,13 +2816,12 @@ static const struct file_operations fops_kp = {
    > static int __init debugfs_kprobe_init(void)
    > {
    > struct dentry *dir;
    > - unsigned int value = 1;
    >
    > dir = debugfs_create_dir("kprobes", NULL);
    >
    > debugfs_create_file("list", 0400, dir, NULL, &kprobes_fops);
    >
    > - debugfs_create_file("enabled", 0600, dir, &value, &fops_kp);
    > + debugfs_create_file("enabled", 0600, dir, NULL, &fops_kp);
    >
    > debugfs_create_file("blacklist", 0400, dir, NULL,
    > &kprobe_blacklist_fops);
    > --
    > 2.30.2
    >


    --
    Masami Hiramatsu <mhiramat@kernel.org>

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