tracing/uprobe: Add support for overlayfs
authorHoward McLauchlan <hmclauchlan@fb.com>
Tue, 10 Apr 2018 23:10:30 +0000 (16:10 -0700)
committerSteven Rostedt (VMware) <rostedt@goodmis.org>
Wed, 11 Apr 2018 15:31:06 +0000 (11:31 -0400)
commitf0a2aa5a2a406d0a57aa9b320ffaa5538672b6c5
tree267ce87e7894db1aa3d42695598e4e4777e19119
parent0a4d0564f0fc377ad0ba66ce214b9b16324aea4b
tracing/uprobe: Add support for overlayfs

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.

Link: http://lkml.kernel.org/r/20180410231030.2720-1-hmclauchlan@fb.com
Reviewed-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Howard McLauchlan <hmclauchlan@fb.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
kernel/trace/trace_uprobe.c