When setting up an fanotify listener, user may request to get fid
information in event instead of an open file descriptor.
The fid obtained with event on a watched object contains the file
handle returned by name_to_handle_at(2) and fsid returned by statfs(2).
When setting a mark, we need to make sure that the filesystem
supports encoding file handles with name_to_handle_at(2) and that
statfs(2) encodes a non-zero fsid.
Cc: <linux-api@xxxxxxxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/notify/fanotify/fanotify_user.c | 54 +++++++++++++++++++++++++++++-
fs/statfs.c | 4 ++-
include/linux/fanotify.h | 2 +-
include/linux/statfs.h | 3 ++
4 files changed, 60 insertions(+), 3 deletions(-)
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index ea8e81a3e80b..d7aa2f392a64 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -17,6 +17,8 @@
#include <linux/compat.h>
#include <linux/sched/signal.h>
#include <linux/memcontrol.h>
+#include <linux/statfs.h>
+#include <linux/exportfs.h>
#include <asm/ioctls.h>
@@ -857,6 +859,49 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
return fd;
}
+/* Check if filesystem can encode a unique fid */
+static int fanotify_test_fid(struct path *path)
+{
+ struct kstatfs stat, root_stat;
+ int err;
+
+ /*
+ * Make sure path is not in filesystem with zero fsid (e.g. tmpfs).
+ * TODO: cache fsid in the mark connector.
+ */
+ err = vfs_statfs(path, &stat);
+ if (err)
+ return err;
+
+ if (!stat.f_fsid.val[0] && !stat.f_fsid.val[1])
+ return -ENODEV;
+
+ /*
+ * Make sure path is not inside a filesystem subvolume (e.g. btrfs)
+ * which uses a different fsid than sb root.
+ */
+ err = statfs_by_dentry(path->dentry->d_sb->s_root, &root_stat);
+ if (err)
+ return err;
+
+ if (root_stat.f_fsid.val[0] != stat.f_fsid.val[0] ||
+ root_stat.f_fsid.val[1] != stat.f_fsid.val[1])
+ return -EXDEV;
+
+ /*
+ * We need to make sure that the file system supports at least
+ * encoding a file handle so user can use name_to_handle_at() to
+ * compare fid returned with event to the file handle of watched
+ * objects. However, name_to_handle_at() requires that the
+ * filesystem also supports decoding file handles.
+ */
+ if (!path->dentry->d_sb->s_export_op ||
+ !path->dentry->d_sb->s_export_op->fh_to_dentry)
+ return -EOPNOTSUPP;
+
+ return 0;
+}
+
static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
int dfd, const char __user *pathname)
{
@@ -942,6 +987,12 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
if (ret)
goto fput_and_out;
+ if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+ ret = fanotify_test_fid(&path);
+ if (ret)
+ goto path_put_and_out;
+ }
+
/* inode held in place by reference to path; group by fget on fd */
if (mark_type == FAN_MARK_INODE)
inode = path.dentry->d_inode;
@@ -970,6 +1021,7 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
ret = -EINVAL;
}
+path_put_and_out:
path_put(&path);
fput_and_out:
fdput(f);
@@ -1006,7 +1058,7 @@ COMPAT_SYSCALL_DEFINE6(fanotify_mark,
*/
static int __init fanotify_user_setup(void)
{
- BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 7);
+ BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 8);
BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);
fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
diff --git a/fs/statfs.c b/fs/statfs.c
index f0216629621d..6a5d840a2d8d 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -50,7 +50,8 @@ static int calculate_f_flags(struct vfsmount *mnt)
flags_by_sb(mnt->mnt_sb->s_flags);
}
-static int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
+/* Does not set buf->f_flags */
+int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
{
int retval;
@@ -66,6 +67,7 @@ static int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
buf->f_frsize = buf->f_bsize;
return retval;
}
+EXPORT_SYMBOL(statfs_by_dentry);
int vfs_statfs(const struct path *path, struct kstatfs *buf)
{
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 9e2142795335..f59be967f72b 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -19,7 +19,7 @@
FAN_CLASS_PRE_CONTENT)
#define FANOTIFY_INIT_FLAGS (FANOTIFY_CLASS_BITS | \
- FAN_REPORT_TID | \
+ FAN_REPORT_TID | FAN_REPORT_FID | \
FAN_CLOEXEC | FAN_NONBLOCK | \
FAN_UNLIMITED_QUEUE | FAN_UNLIMITED_MARKS)
diff --git a/include/linux/statfs.h b/include/linux/statfs.h
index 3142e98546ac..2c3ca7cb8c98 100644
--- a/include/linux/statfs.h
+++ b/include/linux/statfs.h
@@ -41,4 +41,7 @@ struct kstatfs {
#define ST_NODIRATIME 0x0800 /* do not update directory access times */
#define ST_RELATIME 0x1000 /* update atime relative to mtime/ctime */
+struct dentry;
+extern int statfs_by_dentry(struct dentry *dentry, struct kstatfs *stat);
+
#endif
--
2.17.1
