linux-kernel - Re: [BUG][PATCH][2.6.36-rc3] fanotify: Do not ignore result of permission decisions

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Message-ID: <201009080924.04841.tvrtko.ursulin@sophos.com>
Date:	Wed, 8 Sep 2010 09:24:04 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	Eric Paris <eparis@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [BUG][PATCH][2.6.36-rc3] fanotify: Do not ignore result of permission decisions


Improved version of the fix which does not include the check
when permission events are not enabled in configuration and
stops processing if no interesting events remain.

Current code ignores access replies to permission decisions so
fix it in a way which will allow all listeners to still receive
non permission events.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
---
 fs/notify/fsnotify.c             |   32 ++++++++++++++++++++++++--------
 include/linux/fsnotify_backend.h |    4 ++++
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 3680242..2350a53 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -224,7 +224,7 @@ int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
        struct fsnotify_group *inode_group, *vfsmount_group;
        struct fsnotify_event *event = NULL;
        struct vfsmount *mnt;
-       int idx, ret = 0;
+       int idx, ret = 0, res;
        /* global tests shouldn't care about events on child only the specific event */
        __u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);

@@ -275,20 +275,36 @@ int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,

                if (inode_group > vfsmount_group) {
                        /* handle inode */
-                       send_to_group(to_tell, NULL, inode_mark, NULL, mask, data,
-                                     data_is, cookie, file_name, &event);
+                       res = send_to_group(to_tell, NULL, inode_mark, NULL, mask, data,
+                                           data_is, cookie, file_name, &event);
                        /* we didn't use the vfsmount_mark */
                        vfsmount_group = NULL;
                } else if (vfsmount_group > inode_group) {
-                       send_to_group(to_tell, mnt, NULL, vfsmount_mark, mask, data,
-                                     data_is, cookie, file_name, &event);
+                       res = send_to_group(to_tell, mnt, NULL, vfsmount_mark, mask, data,
+                                           data_is, cookie, file_name, &event);
                        inode_group = NULL;
                } else {
-                       send_to_group(to_tell, mnt, inode_mark, vfsmount_mark,
-                                     mask, data, data_is, cookie, file_name,
-                                     &event);
+                       res = send_to_group(to_tell, mnt, inode_mark, vfsmount_mark,
+                                           mask, data, data_is, cookie, file_name,
+                                           &event);
                }

+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+               /* If a listener denied on a permission event we will remember the reason
+                  and run the rest with a non-permission mask only. This allows other
+                  listeners to receive non-permission notifications but we do not care
+                  about further permission checks and want to deny this event. */
+               if (unlikely((res == -EPERM) && (mask & FS_ALL_PERM_EVENTS))) {
+                       mask &= ~FS_ALL_PERM_EVENTS;
+                       ret = res;
+                       /* Stop processing if no interesting events remains. */
+                       if (!(mask & (ALL_FSNOTIFY_EVENTS & ~FS_EVENT_ON_CHILD)))
+                               break;
+               }
+#else
+               (void)res;
+#endif
+
                if (inode_group)
                        inode_node = srcu_dereference(inode_node->next,
                                                      &fsnotify_mark_srcu);
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index e40190d..c8aea03 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -64,6 +64,10 @@

 #define FS_MOVE                        (FS_MOVED_FROM | FS_MOVED_TO)

+/* All events which require a permission response from userspace */
+#define FS_ALL_PERM_EVENTS (FS_OPEN_PERM |\
+                           FS_ACCESS_PERM)
+
 #define ALL_FSNOTIFY_EVENTS (FS_ACCESS | FS_MODIFY | FS_ATTRIB | \
                             FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN | \
                             FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE | \

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