[PATCH] x86/intel_rdt: Fix locking in rdtgroup_schemata_write

[PATCH] x86/intel_rdt: Fix locking in rdtgroup_schemata_write

[Jiri Olsa]

Currently we release the schemata lock before we free the
resource's temporary tmp_cbms allocation, which could be
already used another concurrent access and crashed like:

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: rdtgroup_schemata_write+0x2d1/0x460
  ...
  SNIP
  ...
  rdtgroup_file_write+0x1b/0x30
  kernfs_fop_write+0xe0/0x160
  vfs_write+0xbd/0x1e0
  SyS_write+0x7f/0xe0
  system_call_fastpath+0x16/0x1b

Moving the unlock after the release code.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Shaohua Li <shli@fb.com>
---
 arch/x86/kernel/cpu/intel_rdt_schemata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_schemata.c b/arch/x86/kernel/cpu/intel_rdt_schemata.c
index f369cb8db0d5..badd2b31a560 100644
--- a/arch/x86/kernel/cpu/intel_rdt_schemata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_schemata.c
@@ -200,11 +200,11 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 	}
 
 out:
-	rdtgroup_kn_unlock(of->kn);
 	for_each_enabled_rdt_resource(r) {
 		kfree(r->tmp_cbms);
 		r->tmp_cbms = NULL;
 	}
+	rdtgroup_kn_unlock(of->kn);
 	return ret ?: nbytes;
 }
 
-- 
2.9.3

[tip:x86/urgent] x86/intel_rdt: Fix locking in rdtgroup_schemata_write()

[tip-bot for Jiri Olsa]

Commit-ID:  7f00f388712b29005782bad7e4b25942620f3b9c
Gitweb:     http://git.kernel.org/tip/7f00f388712b29005782bad7e4b25942620f3b9c
Author:     Jiri Olsa <jolsa@kernel.org>
AuthorDate: Tue, 11 Apr 2017 09:14:46 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 11 Apr 2017 09:48:12 +0200

x86/intel_rdt: Fix locking in rdtgroup_schemata_write()

The schemata lock is released before freeing the resource's temporary
tmp_cbms allocation. That's racy versus another write which allocates and
uses new temporary storage, resulting in memory leaks, freeing in use
memory, double a free or any combination of those.

Move the unlock after the release code.

Fixes: 60ec2440c63d ("x86/intel_rdt: Add schemata file")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Shaohua Li <shli@fb.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170411071446.15241-1-jolsa@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/intel_rdt_schemata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_schemata.c b/arch/x86/kernel/cpu/intel_rdt_schemata.c
index f369cb8..badd2b3 100644
--- a/arch/x86/kernel/cpu/intel_rdt_schemata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_schemata.c
@@ -200,11 +200,11 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 	}
 
 out:
-	rdtgroup_kn_unlock(of->kn);
 	for_each_enabled_rdt_resource(r) {
 		kfree(r->tmp_cbms);
 		r->tmp_cbms = NULL;
 	}
+	rdtgroup_kn_unlock(of->kn);
 	return ret ?: nbytes;
 }