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 <[email protected]>
---
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
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 <[email protected]>
Reviewed-by: Josef Bacik <[email protected]>
Thanks,
Josef