[tip:perf/core] perf/core: Fix crash when using HW tracing kernel filters

[tip-bot for Mathieu Poirier]

Commit-ID:  7f635ff187ab6be0b350b3ec06791e376af238ab
Gitweb:     https://git.kernel.org/tip/7f635ff187ab6be0b350b3ec06791e376af238ab
Author:     Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
AuthorDate: Mon, 16 Jul 2018 17:13:51 -0600
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 25 Jul 2018 11:46:22 +0200

perf/core: Fix crash when using HW tracing kernel filters

In function perf_event_parse_addr_filter(), the path::dentry of each struct
perf_addr_filter is left unassigned (as it should be) when the pattern
being parsed is related to kernel space.  But in function
perf_addr_filter_match() the same dentries are given to d_inode() where
the value is not expected to be NULL, resulting in the following splat:

  Unable to handle kernel NULL pointer dereference at virtual address 0000000000000058
  pc : perf_event_mmap+0x2fc/0x5a0
  lr : perf_event_mmap+0x2c8/0x5a0
  Process uname (pid: 2860, stack limit = 0x000000001cbcca37)
  Call trace:
   perf_event_mmap+0x2fc/0x5a0
   mmap_region+0x124/0x570
   do_mmap+0x344/0x4f8
   vm_mmap_pgoff+0xe4/0x110
   vm_mmap+0x2c/0x40
   elf_map+0x60/0x108
   load_elf_binary+0x450/0x12c4
   search_binary_handler+0x90/0x290
   __do_execve_file.isra.13+0x6e4/0x858
   sys_execve+0x3c/0x50
   el0_svc_naked+0x30/0x34

This patch is fixing the problem by introducing a new check in function
perf_addr_filter_match() to see if the filter's dentry is NULL.

Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: acme@xxxxxxxxxx
Cc: miklos@xxxxxxxxxx
Cc: namhyung@xxxxxxxxxx
Cc: songliubraving@xxxxxx
Fixes: 9511bce9fe8e ("perf/core: Fix bad use of igrab()")
Link: http://lkml.kernel.org/r/1531782831-1186-1-git-send-email-mathieu.poirier@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/events/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cdb32cf8e33c..eec2d5fb676b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7337,6 +7337,10 @@ static bool perf_addr_filter_match(struct perf_addr_filter *filter,
 				     struct file *file, unsigned long offset,
 				     unsigned long size)
 {
+	/* d_inode(NULL) won't be equal to any mapped user-space file */
+	if (!filter->path.dentry)
+		return false;
+
 	if (d_inode(filter->path.dentry) != file_inode(file))
 		return false;