[PATCH] uprobe: add support for overlayfs

[PATCH] uprobe: add support for overlayfs

[Howard McLauchlan]

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'

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 <jbacik@fb.com>
Signed-off-by: Howard McLauchlan <hmclauchlan@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)) {
-- 
2.17.0

Re: [PATCH] uprobe: add support for overlayfs

[Steven Rostedt]

On Tue, 10 Apr 2018 16:10:30 -0700
Howard McLauchlan <hmclauchlan@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.

-- 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 <jbacik@fb.com>
> Signed-off-by: Howard McLauchlan <hmclauchlan@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)) {

Re: [PATCH] uprobe: add support for overlayfs

[Masami Hiramatsu]

On Tue, 10 Apr 2018 20:00:59 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 10 Apr 2018 16:10:30 -0700
> Howard McLauchlan <hmclauchlan@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 <mhiramat@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 <jbacik@fb.com>
> > Signed-off-by: Howard McLauchlan <hmclauchlan@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 <mhiramat@kernel.org>

Re: [PATCH] uprobe: add support for overlayfs

[Srikar Dronamraju]

* Steven Rostedt <rostedt@goodmis.org> [2018-04-10 20:00:59]:

> On Tue, 10 Apr 2018 16:10:30 -0700
> Howard McLauchlan <hmclauchlan@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.
> 
> -- 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.
> > 


Looks good to me.

Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> > Reviewed-by: Josef Bacik <jbacik@fb.com>
> > Signed-off-by: Howard McLauchlan <hmclauchlan@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)) {
> 

[PATCH] uprobe: add support for overlayfs

[Howard McLauchlan]

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'

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.

Signed-off-by: Howard McLauchlan <hmclauchlan@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 268029ae1be6..8b86d76c55ee 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)) {
-- 
2.14.1

Re: [PATCH] uprobe: add support for overlayfs

[Josef Bacik]

On Tue, Feb 27, 2018 at 04:40:14PM -0800, Howard McLauchlan 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'
> 
> 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.
> 
> Signed-off-by: Howard McLauchlan <hmclauchlan@fb.com>

Reviewed-by: Josef Bacik <jbacik@fb.com>

Thanks,

Josef