On Tue, 10 Apr 2018 20:00:59 -0400
Steven Rostedt <rost...@goodmis.org> wrote:
> On Tue, 10 Apr 2018 16:10:30 -0700
> Howard McLauchlan <hmclauch...@fb.com> wrote:
>
> > uprobes cannot successfully attach to binaries located in a directory
> > mounted with overlayfs.
> >
> > To verify, create directories for mounting overlayfs
> > (upper,lower,work,merge), move some binary into merge/ and use readelf
> > to obtain some known instruction of the binary. I used /bin/true and the
> > entry instruction(0x13b0):
> >
> > $ mount -t overlay overlay -o
> > lowerdir=lower,upperdir=upper,workdir=work merge
> > $ cd /sys/kernel/debug/tracing
> > $ echo 'p:true_entry PATH_TO_MERGE/merge/true:0x13b0' > uprobe_events
> > $ echo 1 > events/uprobes/true_entry/enable
> >
> > This returns 'bash: echo: write error: Input/output error' and dmesg
> > tells us 'event trace: Could not enable event true_entry'
>
> I tried the above and verified that it is a problem and your patch
> solves it.
>
> Thanks, I'll apply it and start my tests on it.
This looks good to me.
Reviewed-by: Masami Hiramatsu <mhira...@kernel.org>
Thanks!
>
> -- Steve
>
> >
> > This change makes create_trace_uprobe() look for the real inode of a
> > dentry. In the case of normal filesystems, this simplifies to just
> > returning the inode. In the case of overlayfs(and similar fs) we will
> > obtain the underlying dentry and corresponding inode, upon which uprobes
> > can successfully register.
> >
> > Running the example above with the patch applied, we can see that the
> > uprobe is enabled and will output to trace as expected.
> >
> > Reviewed-by: Josef Bacik <jba...@fb.com>
> > Signed-off-by: Howard McLauchlan <hmclauch...@fb.com>
> > ---
> > kernel/trace/trace_uprobe.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > index 2014f4351ae0..17c65fa4136d 100644
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -446,7 +446,7 @@ static int create_trace_uprobe(int argc, char **argv)
> > if (ret)
> > goto fail_address_parse;
> >
> > - inode = igrab(d_inode(path.dentry));
> > + inode = igrab(d_real_inode(path.dentry));
> > path_put(&path);
> >
> > if (!inode || !S_ISREG(inode->i_mode)) {
>
--
Masami Hiramatsu <mhira...@kernel.org>
