diff mbox series

[20/20] fanotify: no external fh buffer in fanotify_name_event

Message ID 20200612093343.5669-21-amir73il@gmail.com
State New
Headers show
Series Prep work for fanotify named events | expand

Commit Message

Amir Goldstein June 12, 2020, 9:33 a.m. UTC
The fanotify_fh struct has an inline buffer of size 12 which is enough
to store the most common local filesystem file handles (e.g. ext4, xfs).
For file handles that do not fit in the inline buffer (e.g. btrfs), an
external buffer is allocated to store the file handle.

When allocating a variable size fanotify_name_event, there is no point
in allocating also an external fh buffer when file handle does not fit
in the inline buffer.

Check required size for encoding fh, preallocate an event buffer
sufficient to contain both file handle and name and store the name at
name_offset after the file handle.

At this time, when not reporting name in event, we still allocate
the fixed size fanotify_fid_event and an external buffer for large
file handles, but fanotify_alloc_name_event() has already been prepared
to accept a NULL file_name.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c | 72 ++++++++++++++++++++++++-----------
 fs/notify/fanotify/fanotify.h |  4 ++
 2 files changed, 53 insertions(+), 23 deletions(-)
diff mbox series

Patch

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 3a2d48edaddd..c3986fbb6801 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -281,10 +281,22 @@  static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 	return test_mask & user_mask;
 }
 
+static unsigned int fanotify_encode_fh_len(struct inode *inode)
+{
+	int dwords = 0;
+
+	if (!inode)
+		return 0;
+
+	exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
+
+	return dwords << 2;
+}
+
 static void fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
-			       gfp_t gfp)
+			       unsigned int prealloc_fh_len, gfp_t gfp)
 {
-	int dwords, type, bytes = 0;
+	int dwords, bytes, type = 0;
 	char *ext_buf = NULL;
 	void *buf = fh->buf;
 	int err;
@@ -293,15 +305,21 @@  static void fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
 	if (!inode)
 		return;
 
-	dwords = 0;
+	/*
+	 * !gpf means preallocated variable size fh, but prealloc_fh_len could
+	 * be zero in that case if encoding fh len failed.
+	 */
 	err = -ENOENT;
-	type = exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
-	if (!dwords)
+	if (!gfp)
+		bytes = prealloc_fh_len;
+	else
+		bytes = fanotify_encode_fh_len(inode);
+	if (bytes < 4 || WARN_ON_ONCE(bytes % 4))
 		goto out_err;
 
-	bytes = dwords << 2;
-	if (bytes > FANOTIFY_INLINE_FH_LEN) {
-		/* Treat failure to allocate fh as failure to allocate event */
+	/* No external buffer in a variable size allocated fh */
+	if (gfp && bytes > FANOTIFY_INLINE_FH_LEN) {
+		/* Treat failure to allocate fh as failure to encode fh */
 		err = -ENOMEM;
 		ext_buf = kmalloc(bytes, gfp);
 		if (!ext_buf)
@@ -311,17 +329,19 @@  static void fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
 		buf = ext_buf;
 	}
 
+	dwords = bytes >> 2;
 	type = exportfs_encode_inode_fh(inode, buf, &dwords, NULL);
 	err = -EINVAL;
-	if (!type || type == FILEID_INVALID || bytes != dwords << 2)
+	if (!type || type == FILEID_INVALID || bytes < (dwords << 2))
 		goto out_err;
 
 	fh->type = type;
-	fh->len = bytes;
-	if (fh->len > FANOTIFY_INLINE_FH_LEN)
-		fh->name_offset = FANOTIFY_INLINE_FH_LEN;
-	else
-		fh->name_offset = fh->len;
+	fh->len = dwords << 2;
+	/*
+	 * name_offset is set to preallocated fh len, even if actual fh len
+	 * is shorter.
+	 */
+	fh->name_offset = prealloc_fh_len;
 
 	return;
 
@@ -398,7 +418,7 @@  struct fanotify_event *fanotify_alloc_fid_event(struct inode *id,
 
 	ffe->fae.type = FANOTIFY_EVENT_TYPE_FID;
 	ffe->fsid = *fsid;
-	fanotify_encode_fh(&ffe->object_fh, id, gfp);
+	fanotify_encode_fh(&ffe->object_fh, id, 0, gfp);
 
 	return &ffe->fae;
 }
@@ -410,16 +430,26 @@  struct fanotify_event *fanotify_alloc_name_event(struct inode *id,
 {
 	struct fanotify_name_event *fne;
 	struct fanotify_fh *dfh;
+	unsigned int prealloc_fh_len = fanotify_encode_fh_len(id);
+	unsigned int size;
 
-	fne = kmalloc(sizeof(*fne) + file_name->len + 1, gfp);
+	size = sizeof(*fne) - FANOTIFY_INLINE_FH_LEN + prealloc_fh_len;
+	if (file_name)
+		size += file_name->len + 1;
+	fne = kmalloc(size, gfp);
 	if (!fne)
 		return NULL;
 
 	fne->fae.type = FANOTIFY_EVENT_TYPE_FID_NAME;
 	fne->fsid = *fsid;
 	dfh = &fne->dir_fh;
-	fanotify_encode_fh(dfh, id, gfp);
-	fanotify_fh_copy_name(dfh, file_name);
+	fanotify_encode_fh(dfh, id, prealloc_fh_len, 0);
+	if (file_name)
+		fanotify_fh_copy_name(dfh, file_name);
+
+	pr_debug("%s: ino=%lu size=%u prealloc_fh_len=%u dir_fh_len=%u name_len=%u name='%.*s'\n",
+		 __func__, id->i_ino, size, prealloc_fh_len, dfh->len,
+		 dfh->name_len, dfh->name_len, fanotify_fh_name(dfh));
 
 	return &fne->fae;
 }
@@ -634,11 +664,7 @@  static void fanotify_free_fid_event(struct fanotify_event *event)
 
 static void fanotify_free_name_event(struct fanotify_event *event)
 {
-	struct fanotify_name_event *fne = FANOTIFY_NE(event);
-
-	if (fanotify_fh_has_ext_buf(&fne->dir_fh))
-		kfree(fanotify_fh_ext_buf(&fne->dir_fh));
-	kfree(fne);
+	kfree(FANOTIFY_NE(event));
 }
 
 static void fanotify_free_event(struct fsnotify_event *fsn_event)
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 8cb062eefd3e..7cbdac4be42f 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -43,6 +43,10 @@  static inline void fanotify_fh_init(struct fanotify_fh *fh)
 
 static inline bool fanotify_fh_has_ext_buf(struct fanotify_fh *fh)
 {
+	/* No external buffer in a variable size allocated fh */
+	if (fh->name_offset)
+		return false;
+
 	return fh->len > FANOTIFY_INLINE_FH_LEN;
 }