fanotify: use helpers to parcel fanotify_info buffer

fanotify_info buffer is parceled into variable sized records, so the
records must be written in order: dir_fh, file_fh, name.

Use helpers to assert that order and make fanotify_alloc_name_event()
a bit more generic to allow empty dir_fh record and to allow expanding
to more records (i.e. name2) soon.

Link: https://lore.kernel.org/r/20211129201537.1932819-7-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index ffad224..2b13c79 100644 (file)
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -576,7 +576,7 @@ static struct fanotify_event *fanotify_alloc_fid_event(struct inode *id,
        return &ffe->fae;
 }
 
-static struct fanotify_event *fanotify_alloc_name_event(struct inode *id,
+static struct fanotify_event *fanotify_alloc_name_event(struct inode *dir,
                                                        __kernel_fsid_t *fsid,
                                                        const struct qstr *name,
                                                        struct inode *child,
@@ -586,15 +586,17 @@ static struct fanotify_event *fanotify_alloc_name_event(struct inode *id,
        struct fanotify_name_event *fne;
        struct fanotify_info *info;
        struct fanotify_fh *dfh, *ffh;
-       unsigned int dir_fh_len = fanotify_encode_fh_len(id);
+       unsigned int dir_fh_len = fanotify_encode_fh_len(dir);
        unsigned int child_fh_len = fanotify_encode_fh_len(child);
-       unsigned int size;
+       unsigned long name_len = name ? name->len : 0;
+       unsigned int len, size;
 
-       size = sizeof(*fne) + FANOTIFY_FH_HDR_LEN + dir_fh_len;
+       /* Reserve terminating null byte even for empty name */
+       size = sizeof(*fne) + name_len + 1;
+       if (dir_fh_len)
+               size += FANOTIFY_FH_HDR_LEN + dir_fh_len;
        if (child_fh_len)
                size += FANOTIFY_FH_HDR_LEN + child_fh_len;
-       if (name)
-               size += name->len + 1;
        fne = kmalloc(size, gfp);
        if (!fne)
                return NULL;
@@ -604,22 +606,23 @@ static struct fanotify_event *fanotify_alloc_name_event(struct inode *id,
        *hash ^= fanotify_hash_fsid(fsid);
        info = &fne->info;
        fanotify_info_init(info);
-       dfh = fanotify_info_dir_fh(info);
-       info->dir_fh_totlen = fanotify_encode_fh(dfh, id, dir_fh_len, hash, 0);
+       if (dir_fh_len) {
+               dfh = fanotify_info_dir_fh(info);
+               len = fanotify_encode_fh(dfh, dir, dir_fh_len, hash, 0);
+               fanotify_info_set_dir_fh(info, len);
+       }
        if (child_fh_len) {
                ffh = fanotify_info_file_fh(info);
-               info->file_fh_totlen = fanotify_encode_fh(ffh, child,
-                                                       child_fh_len, hash, 0);
+               len = fanotify_encode_fh(ffh, child, child_fh_len, hash, 0);
+               fanotify_info_set_file_fh(info, len);
        }
-       if (name) {
-               long salt = name->len;
-
+       if (name_len) {
                fanotify_info_copy_name(info, name);
-               *hash ^= full_name_hash((void *)salt, name->name, name->len);
+               *hash ^= full_name_hash((void *)name_len, name->name, name_len);
        }
 
-       pr_debug("%s: ino=%lu size=%u dir_fh_len=%u child_fh_len=%u name_len=%u name='%.*s'\n",
-                __func__, id->i_ino, size, dir_fh_len, child_fh_len,
+       pr_debug("%s: size=%u dir_fh_len=%u child_fh_len=%u name_len=%u name='%.*s'\n",
+                __func__, size, dir_fh_len, child_fh_len,
                 info->name_len, info->name_len, fanotify_info_name(info));
 
        return &fne->fae;

diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index dd23ba6..7ac6f9f 100644 (file)
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -138,6 +138,26 @@ static inline void fanotify_info_init(struct fanotify_info *info)
        info->name_len = 0;
 }
 
+/* These set/copy helpers MUST be called by order */
+static inline void fanotify_info_set_dir_fh(struct fanotify_info *info,
+                                           unsigned int totlen)
+{
+       if (WARN_ON_ONCE(info->file_fh_totlen > 0) ||
+           WARN_ON_ONCE(info->name_len > 0))
+               return;
+
+       info->dir_fh_totlen = totlen;
+}
+
+static inline void fanotify_info_set_file_fh(struct fanotify_info *info,
+                                            unsigned int totlen)
+{
+       if (WARN_ON_ONCE(info->name_len > 0))
+               return;
+
+       info->file_fh_totlen = totlen;
+}
+
 static inline void fanotify_info_copy_name(struct fanotify_info *info,
                                           const struct qstr *name)
 {