[v2,02/16] fsnotify: introduce pre-content permission event

Commit Message

Josef Bacik Aug. 8, 2024, 7:27 p.m. UTC

From: Amir Goldstein <[e-mail]>

The new FS_PRE_ACCESS permission event is similar to FS_ACCESS_PERM,
but it meant for a different use case of filling file content before
access to a file range, so it has slightly different semantics.

Generate FS_PRE_ACCESS/FS_ACCESS_PERM as two seperate events, same as
we did for FS_OPEN_PERM/FS_OPEN_EXEC_PERM.

FS_PRE_MODIFY is a new permission event, with similar semantics as
FS_PRE_ACCESS, which is called before a file is modified.

FS_ACCESS_PERM is reported also on blockdev and pipes, but the new
pre-content events are only reported for regular files and dirs.

The pre-content events are meant to be used by hierarchical storage
managers that want to fill the content of files on first access.

Signed-off-by: Amir Goldstein <[e-mail]>
---
 fs/notify/fsnotify.c             |  2 +-
 include/linux/fsnotify.h         | 27 ++++++++++++++++++++++++---
 include/linux/fsnotify_backend.h | 13 +++++++++++--
 security/selinux/hooks.c         |  3 ++-
 4 files changed, 38 insertions(+), 7 deletions(-)

Patch

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 272c8a1dab3c..1ca4a8da7f29 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -621,7 +621,7 @@  static __init int fsnotify_init(void)
 {
 	int ret;
 
-	BUILD_BUG_ON(HWEIGHT32(ALL_FSNOTIFY_BITS) != 23);
+	BUILD_BUG_ON(HWEIGHT32(ALL_FSNOTIFY_BITS) != 25);
 
 	ret = init_srcu_struct(&fsnotify_mark_srcu);
 	if (ret)
diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 278620e063ab..028ce807805a 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -133,12 +133,13 @@  static inline int fsnotify_file(struct file *file, __u32 mask)
 
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
 /*
- * fsnotify_file_area_perm - permission hook before access to file range
+ * fsnotify_file_area_perm - permission hook before access/modify of file range
  */
 static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
 					  const loff_t *ppos, size_t count)
 {
-	__u32 fsnotify_mask = FS_ACCESS_PERM;
+	struct inode *inode = file_inode(file);
+	__u32 fsnotify_mask;
 
 	/*
 	 * filesystem may be modified in the context of permission events
@@ -147,7 +148,27 @@  static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
 	 */
 	lockdep_assert_once(file_write_not_started(file));
 
-	if (!(perm_mask & MAY_READ))
+	/*
+	 * Generate FS_PRE_ACCESS/FS_ACCESS_PERM as two seperate events.
+	 */
+	if (perm_mask & MAY_READ) {
+		int ret = fsnotify_file(file, FS_ACCESS_PERM);
+
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * Pre-content events are only reported for regular files and dirs.
+	 */
+	if (!S_ISDIR(inode->i_mode) && !S_ISREG(inode->i_mode))
+		return 0;
+
+	if (perm_mask & MAY_WRITE)
+		fsnotify_mask = FS_PRE_MODIFY;
+	else if (perm_mask & MAY_READ)
+		fsnotify_mask = FS_PRE_ACCESS;
+	else
 		return 0;
 
 	return fsnotify_file(file, fsnotify_mask);
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 8be029bc50b1..200a5e3b1cd4 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -56,6 +56,9 @@ 
 #define FS_ACCESS_PERM		0x00020000	/* access event in a permissions hook */
 #define FS_OPEN_EXEC_PERM	0x00040000	/* open/exec event in a permission hook */
 
+#define FS_PRE_ACCESS		0x00080000	/* Pre-content access hook */
+#define FS_PRE_MODIFY		0x00100000	/* Pre-content modify hook */
+
 /*
  * Set on inode mark that cares about things that happen to its children.
  * Always set for dnotify and inotify.
@@ -77,8 +80,14 @@ 
  */
 #define ALL_FSNOTIFY_DIRENT_EVENTS (FS_CREATE | FS_DELETE | FS_MOVE | FS_RENAME)
 
-#define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM | \
-				  FS_OPEN_EXEC_PERM)
+/* Content events can be used to inspect file content */
+#define FSNOTIFY_CONTENT_PERM_EVENTS (FS_OPEN_PERM | FS_OPEN_EXEC_PERM | \
+				      FS_ACCESS_PERM)
+/* Pre-content events can be used to fill file content */
+#define FSNOTIFY_PRE_CONTENT_EVENTS  (FS_PRE_ACCESS | FS_PRE_MODIFY)
+
+#define ALL_FSNOTIFY_PERM_EVENTS (FSNOTIFY_CONTENT_PERM_EVENTS | \
+				  FSNOTIFY_PRE_CONTENT_EVENTS)
 
 /*
  * This is a list of all events that may get sent to a parent that is watching
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 55c78c318ccd..2997edf3e7cd 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3406,7 +3406,8 @@  static int selinux_path_notify(const struct path *path, u64 mask,
 		perm |= FILE__WATCH_WITH_PERM;
 
 	/* watches on read-like events need the file:watch_reads permission */
-	if (mask & (FS_ACCESS | FS_ACCESS_PERM | FS_CLOSE_NOWRITE))
+	if (mask & (FS_ACCESS | FS_ACCESS_PERM | FS_PRE_ACCESS |
+		    FS_CLOSE_NOWRITE))
 		perm |= FILE__WATCH_READS;
 
 	return path_has_perm(current_cred(), path, perm);