[PATCH v2 4/9] fanotify: encode file identifier for FAN_REPORT_FID

[Amir Goldstein <amir73il@xxxxxxxxx>]

Allocate and encode event->info.fid for a group with FAN_REPORT_FID.
Treat failure to allocate fid buffer as failure to allocate event.
Treat failure to encode fid by printing a warning but queueing
the event without the fid information.

Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 fs/notify/fanotify/fanotify.c | 59 +++++++++++++++++++++++++++++++++--
 1 file changed, 57 insertions(+), 2 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 8192d4b1db21..844b748f0b74 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -13,6 +13,8 @@
 #include <linux/wait.h>
 #include <linux/audit.h>
 #include <linux/sched/mm.h>
+#include <linux/statfs.h>
+#include <linux/exportfs.h>
 
 #include "fanotify.h"
 
@@ -146,11 +148,55 @@ static u32 fanotify_group_event_mask(struct fsnotify_iter_info *iter_info,
 		~marks_ignored_mask;
 }
 
+static struct fanotify_event_fid *fanotify_alloc_fid(const struct path *path,
+						     gfp_t gfp)
+{
+	struct fanotify_event_fid *fid = NULL;
+	int dwords, bytes = 0;
+	struct kstatfs stat;
+	int err, type;
+
+	dwords = 0;
+	err = -ENOENT;
+	type = exportfs_encode_fh(path->dentry, NULL, &dwords,  0);
+	if (!dwords)
+		goto out_err;
+
+	err = vfs_statfs(path, &stat);
+	if (err)
+		goto out_err;
+
+	/* Treat failure to allocate fid as failure to allocate event */
+	bytes = dwords << 2;
+	fid = kmalloc(FANOTIFY_FID_LEN(bytes), gfp);
+	if (!fid)
+		return NULL;
+
+	type = exportfs_encode_fh(path->dentry, (struct fid *)fid->f_handle,
+				  &dwords,  0);
+	err = -EINVAL;
+	if (type == FILEID_INVALID || bytes != dwords << 2)
+		goto out_err;
+
+	fid->handle_bytes = bytes;
+	fid->handle_type = type;
+	fid->fsid = stat.f_fsid;
+
+	return fid;
+
+out_err:
+	pr_warn_ratelimited("fanotify: failed to encode fid of %pd2 (bytes=%d, err=%i)\n",
+			    path->dentry, bytes, err);
+	kfree(fid);
+	return ERR_PTR(err);
+}
+
 struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 						 struct inode *inode, u32 mask,
 						 const struct path *path)
 {
 	struct fanotify_event *event = NULL;
+	struct fanotify_event_fid *fid = NULL;
 	gfp_t gfp = GFP_KERNEL_ACCOUNT;
 
 	/*
@@ -164,6 +210,16 @@ struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 	/* Whoever is interested in the event, pays for the allocation. */
 	memalloc_use_memcg(group->memcg);
 
+	if (path && FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+		fid = fanotify_alloc_fid(path, gfp);
+		/* Treat failure to allocate fid as failure to allocate event */
+		if (!fid)
+			goto out;
+		/* Report the event without a file identifier on encode error */
+		if (IS_ERR(fid))
+			fid = NULL;
+	}
+
 	if (fanotify_is_perm_event(mask)) {
 		struct fanotify_perm_event *pevent;
 
@@ -184,8 +240,7 @@ init: __maybe_unused
 	else
 		event->pid = get_pid(task_tgid(current));
 	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
-		/* TODO: allocate buffer and encode file handle */
-		fanotify_set_fid(event, NULL);
+		fanotify_set_fid(event, fid);
 	} else if (path) {
 		event->path = *path;
 		path_get(&event->path);
-- 
2.17.1