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SubjectRe: [PATCH] CRED: Fix check_unsafe_exec()
Date
Hugh Dickins <hugh@veritas.com> wrote:

> We do. See the original thread. It's here at
> http://lkml.org/lkml/2009/2/26/233
> and appended below for convenience. We do know that patch did not
> fix Joe's problem, and we don't yet know whether addressing the
> files->count issue will actually fix it, but I'm hopeful.

Looks reasonable. One thing that should be added, though, is a comment in
struct fs_struct to give a warning about the consequences of incrementing the
usage count for anything other than CLONE_FS.

David
---
From: David Howells <dhowells@redhat.com>
Subject: [PATCH] Annotate struct fs_struct's usage count to indicate the restrictions upon it

Annotate struct fs_struct's usage count to indicate the restrictions upon it.
It may not be incremented, except by clone(CLONE_FS), as this affects the
check in check_unsafe_exec() in fs/exec.c.

Signed-off-by: David Howells <dhowells@redhat.com>
---

include/linux/fs_struct.h | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)


diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h
index a97c053..b12ede4 100644
--- a/include/linux/fs_struct.h
+++ b/include/linux/fs_struct.h
@@ -4,7 +4,11 @@
#include <linux/path.h>

struct fs_struct {
- atomic_t count;
+ atomic_t count; /* This usage count is used by check_unsafe_exec() for
+ * security checking purposes - therefore it may not be
+ * incremented, except by clone(CLONE_FS).
+ */
+
rwlock_t lock;
int umask;
struct path root, pwd;

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