From: Amir Goldstein <amir73il@xxxxxxxxx> Legacy inotify/fanotify listeners can add watches for events on inode, parent or mount and expect to get events (e.g. FS_MODIFY) on files that were already open at the time of setting up the watches. fanotify permission events are typically used by Anti-malware sofware, that is watching the entire mount and it is not common to have more that one Anti-malware engine installed on a system. To reduce the overhead of the fsnotify_file_perm() hooks on every file access, relax the semantics of the legacy FAN_OPEN_PERM event to generate events only if there were *any* permission event listeners on the filesystem at the time that the file was open. The new semantics, implemented with the opt-in FMODE_NOTIFY_PERM flag are also going to apply to the new fanotify pre-content event in order to reduce the cost of the pre-content event vfs hooks. Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wj8L=mtcRTi=NECHMGfZQgXOp_uix1YVh04fEmrKaMnXA@xxxxxxxxxxxxxx/ Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> --- include/linux/fs.h | 3 ++- include/linux/fsnotify.h | 47 ++++++++++++++++++++++++++++------------ 2 files changed, 35 insertions(+), 15 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 9c13222362f5..9b58e9887e4b 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -173,7 +173,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, #define FMODE_NOREUSE ((__force fmode_t)(1 << 23)) -/* FMODE_* bit 24 */ +/* File may generate fanotify access permission events */ +#define FMODE_NOTIFY_PERM ((__force fmode_t)(1 << 24)) /* File is embedded in backing_file object */ #define FMODE_BACKING ((__force fmode_t)(1 << 25)) diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h index 278620e063ab..f0fd3dcae654 100644 --- a/include/linux/fsnotify.h +++ b/include/linux/fsnotify.h @@ -108,10 +108,9 @@ static inline void fsnotify_dentry(struct dentry *dentry, __u32 mask) fsnotify_parent(dentry, mask, dentry, FSNOTIFY_EVENT_DENTRY); } -static inline int fsnotify_file(struct file *file, __u32 mask) +/* Should events be generated on this open file regardless of watches? */ +static inline bool fsnotify_file_watchable(struct file *file, __u32 mask) { - const struct path *path; - /* * FMODE_NONOTIFY are fds generated by fanotify itself which should not * generate new events. We also don't want to generate events for @@ -119,14 +118,37 @@ static inline int fsnotify_file(struct file *file, __u32 mask) * handle creation / destruction events and not "real" file events. */ if (file->f_mode & (FMODE_NONOTIFY | FMODE_PATH)) + return false; + + /* Permission events require that watches are set before FS_OPEN_PERM */ + if (mask & ALL_FSNOTIFY_PERM_EVENTS & ~FS_OPEN_PERM && + !(file->f_mode & FMODE_NOTIFY_PERM)) + return false; + + return true; +} + +static inline int fsnotify_file(struct file *file, __u32 mask) +{ + const struct path *path; + + if (!fsnotify_file_watchable(file, mask)) return 0; path = &file->f_path; - /* Permission events require group prio >= FSNOTIFY_PRIO_CONTENT */ - if (mask & ALL_FSNOTIFY_PERM_EVENTS && - !fsnotify_sb_has_priority_watchers(path->dentry->d_sb, - FSNOTIFY_PRIO_CONTENT)) - return 0; + /* + * Permission events require group prio >= FSNOTIFY_PRIO_CONTENT. + * Unless permission event watchers exist at FS_OPEN_PERM time, + * operations on file will not be generating any permission events. + */ + if (mask & ALL_FSNOTIFY_PERM_EVENTS) { + if (!fsnotify_sb_has_priority_watchers(path->dentry->d_sb, + FSNOTIFY_PRIO_CONTENT)) + return 0; + + if (mask & FS_OPEN_PERM) + file->f_mode |= FMODE_NOTIFY_PERM; + } return fsnotify_parent(path->dentry, mask, path, FSNOTIFY_EVENT_PATH); } @@ -166,15 +188,12 @@ static inline int fsnotify_file_perm(struct file *file, int perm_mask) */ static inline int fsnotify_open_perm(struct file *file) { - int ret; + int ret = fsnotify_file(file, FS_OPEN_PERM); - if (file->f_flags & __FMODE_EXEC) { + if (!ret && file->f_flags & __FMODE_EXEC) ret = fsnotify_file(file, FS_OPEN_EXEC_PERM); - if (ret) - return ret; - } - return fsnotify_file(file, FS_OPEN_PERM); + return ret; } #else -- 2.43.0
