fanotify: introduce FAN_PRE_ACCESS permission event

Similar to FAN_ACCESS_PERM permission event, but it is only allowed with
class FAN_CLASS_PRE_CONTENT and only allowed on regular files and dirs.

Unlike FAN_ACCESS_PERM, it is safe to write to the file being accessed
in the context of the event handler.

This pre-content event is meant to be used by hierarchical storage
managers that want to fill the content of files on first read access.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/b80986f8d5b860acea2c9a73c0acd93587be5fe4.1731684329.git.josef@toxicpanda.com

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 2e6ba94ec4056335beea29c7b2e1e0f8ff74db6f..da6c3c1c7edf51e7c08b51f36678a202614be691 100644 (file)
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -916,8 +916,9 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
        BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);
        BUILD_BUG_ON(FAN_FS_ERROR != FS_ERROR);
        BUILD_BUG_ON(FAN_RENAME != FS_RENAME);
+       BUILD_BUG_ON(FAN_PRE_ACCESS != FS_PRE_ACCESS);
 
-       BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 21);
+       BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 22);
 
        mask = fanotify_group_event_mask(group, iter_info, &match_mask,
                                         mask, data, data_type, dir);

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 456cc3e92c8832763eaee5c92870498f07612bca..08e4d8659ef51a3fdb785b0531aac1e4484d95f4 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -1287,7 +1287,7 @@ static int fanotify_group_init_error_pool(struct fsnotify_group *group)
 }
 
 static int fanotify_may_update_existing_mark(struct fsnotify_mark *fsn_mark,
-                                             unsigned int fan_flags)
+                                            __u32 mask, unsigned int fan_flags)
 {
        /*
         * Non evictable mark cannot be downgraded to evictable mark.
@@ -1314,6 +1314,11 @@ static int fanotify_may_update_existing_mark(struct fsnotify_mark *fsn_mark,
            fsn_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY)
                return -EEXIST;
 
+       /* For now pre-content events are not generated for directories */
+       mask |= fsn_mark->mask;
+       if (mask & FANOTIFY_PRE_CONTENT_EVENTS && mask & FAN_ONDIR)
+               return -EEXIST;
+
        return 0;
 }
 
@@ -1340,7 +1345,7 @@ static int fanotify_add_mark(struct fsnotify_group *group,
        /*
         * Check if requested mark flags conflict with an existing mark flags.
         */
-       ret = fanotify_may_update_existing_mark(fsn_mark, fan_flags);
+       ret = fanotify_may_update_existing_mark(fsn_mark, mask, fan_flags);
        if (ret)
                goto out;
 
@@ -1640,11 +1645,23 @@ static int fanotify_events_supported(struct fsnotify_group *group,
                                     unsigned int flags)
 {
        unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
+       bool is_dir = d_is_dir(path->dentry);
        /* Strict validation of events in non-dir inode mask with v5.17+ APIs */
        bool strict_dir_events = FAN_GROUP_FLAG(group, FAN_REPORT_TARGET_FID) ||
                                 (mask & FAN_RENAME) ||
                                 (flags & FAN_MARK_IGNORE);
 
+       /*
+        * Filesystems need to opt-into pre-content evnets (a.k.a HSM)
+        * and they are only supported on regular files and directories.
+        */
+       if (mask & FANOTIFY_PRE_CONTENT_EVENTS) {
+               if (!(path->mnt->mnt_sb->s_iflags & SB_I_ALLOW_HSM))
+                       return -EOPNOTSUPP;
+               if (!is_dir && !d_is_reg(path->dentry))
+                       return -EINVAL;
+       }
+
        /*
         * Some filesystems such as 'proc' acquire unusual locks when opening
         * files. For them fanotify permission events have high chances of
@@ -1677,7 +1694,7 @@ static int fanotify_events_supported(struct fsnotify_group *group,
         * but because we always allowed it, error only when using new APIs.
         */
        if (strict_dir_events && mark_type == FAN_MARK_INODE &&
-           !d_is_dir(path->dentry) && (mask & FANOTIFY_DIRONLY_EVENT_BITS))
+           !is_dir && (mask & FANOTIFY_DIRONLY_EVENT_BITS))
                return -ENOTDIR;
 
        return 0;
@@ -1778,10 +1795,14 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
                return -EPERM;
 
        /*
-        * Permission events require minimum priority FAN_CLASS_CONTENT.
+        * Permission events are not allowed for FAN_CLASS_NOTIF.
+        * Pre-content permission events are not allowed for FAN_CLASS_CONTENT.
         */
        if (mask & FANOTIFY_PERM_EVENTS &&
-           group->priority < FSNOTIFY_PRIO_CONTENT)
+           group->priority == FSNOTIFY_PRIO_NORMAL)
+               return -EINVAL;
+       else if (mask & FANOTIFY_PRE_CONTENT_EVENTS &&
+                group->priority == FSNOTIFY_PRIO_CONTENT)
                return -EINVAL;
 
        if (mask & FAN_FS_ERROR &&
@@ -1816,6 +1837,10 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
        if (mask & FAN_RENAME && !(fid_mode & FAN_REPORT_NAME))
                return -EINVAL;
 
+       /* Pre-content events are not currently generated for directories. */
+       if (mask & FANOTIFY_PRE_CONTENT_EVENTS && mask & FAN_ONDIR)
+               return -EINVAL;
+
        if (mark_cmd == FAN_MARK_FLUSH) {
                if (mark_type == FAN_MARK_MOUNT)
                        fsnotify_clear_vfsmount_marks_by_group(group);

diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 89ff45bd6f01baad88eb8328675e27133fc797a6..c747af064d2c6dc0418eb9c20cc169b4b064dc89 100644 (file)
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -89,6 +89,16 @@
 #define FANOTIFY_DIRENT_EVENTS (FAN_MOVE | FAN_CREATE | FAN_DELETE | \
                                 FAN_RENAME)
 
+/* Content events can be used to inspect file content */
+#define FANOTIFY_CONTENT_PERM_EVENTS (FAN_OPEN_PERM | FAN_OPEN_EXEC_PERM | \
+                                     FAN_ACCESS_PERM)
+/* Pre-content events can be used to fill file content */
+#define FANOTIFY_PRE_CONTENT_EVENTS  (FAN_PRE_ACCESS)
+
+/* Events that require a permission response from user */
+#define FANOTIFY_PERM_EVENTS   (FANOTIFY_CONTENT_PERM_EVENTS | \
+                                FANOTIFY_PRE_CONTENT_EVENTS)
+
 /* Events that can be reported with event->fd */
 #define FANOTIFY_FD_EVENTS (FANOTIFY_PATH_EVENTS | FANOTIFY_PERM_EVENTS)
 
@@ -104,10 +114,6 @@
                                 FANOTIFY_INODE_EVENTS | \
                                 FANOTIFY_ERROR_EVENTS)
 
-/* Events that require a permission response from user */
-#define FANOTIFY_PERM_EVENTS   (FAN_OPEN_PERM | FAN_ACCESS_PERM | \
-                                FAN_OPEN_EXEC_PERM)
-
 /* Extra flags that may be reported with event or control handling of events */
 #define FANOTIFY_EVENT_FLAGS   (FAN_EVENT_ON_CHILD | FAN_ONDIR)
 

diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 79072b6894f25a4b9990f8bccf712d034f1b4ddc..7596168c80ebf0d5fa3b9d8b2a241d154bd3ee85 100644 (file)
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -27,6 +27,8 @@
 #define FAN_OPEN_EXEC_PERM     0x00040000      /* File open/exec in perm check */
 /* #define FAN_DIR_MODIFY      0x00080000 */   /* Deprecated (reserved) */
 
+#define FAN_PRE_ACCESS         0x00100000      /* Pre-content access hook */
+
 #define FAN_EVENT_ON_CHILD     0x08000000      /* Interested in child events */
 
 #define FAN_RENAME             0x10000000      /* File was renamed */