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fanotify: check file flags passed in fanotify_init
Without this patch fanotify_init does not validate the value passed in event_f_flags. When a fanotify event is read from the fanotify file descriptor a new file descriptor is created where file.f_flags = event_f_flags. Internal and external open flags are stored together in field f_flags of struct file. Hence, an application might create file descriptors with internal flags like FMODE_EXEC, FMODE_NOCMTIME set. Jan Kara and Eric Paris both aggreed that this is a bug and the value of event_f_flags should be checked: https://lkml.org/lkml/2014/4/29/522 https://lkml.org/lkml/2014/4/29/539 This updated patch version considers the comments by Michael Kerrisk in https://lkml.org/lkml/2014/5/4/10 With the patch the value of event_f_flags is checked. When specifying an invalid value error EINVAL is returned. Internal flags are disallowed. File creation flags are disallowed: O_CREAT, O_DIRECTORY, O_EXCL, O_NOCTTY, O_NOFOLLOW, O_TRUNC, and O_TTY_INIT. Flags which do not make sense with fanotify are disallowed: __O_TMPFILE, O_PATH, FASYNC, and O_DIRECT. This leaves us with the following allowed values: O_RDONLY, O_WRONLY, O_RDWR are basic functionality. The are stored in the bits given by O_ACCMODE. O_APPEND is working as expected. The value might be useful in a logging application which appends the current status each time the log is opened. O_LARGEFILE is needed for files exceeding 4GB on 32bit systems. O_NONBLOCK may be useful when monitoring slow devices like tapes. O_NDELAY is equal to O_NONBLOCK except for platform parisc. To avoid code breaking on parisc either both flags should be allowed or none. The patch allows both. __O_SYNC and O_DSYNC may be used to avoid data loss on power disruption. O_NOATIME may be useful to reduce disk activity. O_CLOEXEC may be useful, if separate processes shall be used to scan files. Once this patch is accepted, the fanotify_init.2 manpage has to be updated. Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -25,6 +25,19 @@
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#define FANOTIFY_DEFAULT_MAX_MARKS 8192
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#define FANOTIFY_DEFAULT_MAX_LISTENERS 128
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/*
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* All flags that may be specified in parameter event_f_flags of fanotify_init.
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*
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* Internal and external open flags are stored together in field f_flags of
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* struct file. Only external open flags shall be allowed in event_f_flags.
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* Internal flags like FMODE_NONOTIFY, FMODE_EXEC, FMODE_NOCMTIME shall be
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* excluded.
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*/
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#define FANOTIFY_INIT_ALL_EVENT_F_BITS ( \
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O_ACCMODE | O_APPEND | O_NONBLOCK | \
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__O_SYNC | O_DSYNC | O_CLOEXEC | \
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O_LARGEFILE | O_NOATIME )
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extern const struct fsnotify_ops fanotify_fsnotify_ops;
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static struct kmem_cache *fanotify_mark_cache __read_mostly;
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@ -669,6 +682,18 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
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if (flags & ~FAN_ALL_INIT_FLAGS)
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return -EINVAL;
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if (event_f_flags & ~FANOTIFY_INIT_ALL_EVENT_F_BITS)
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return -EINVAL;
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switch (event_f_flags & O_ACCMODE) {
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case O_RDONLY:
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case O_RDWR:
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case O_WRONLY:
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break;
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default:
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return -EINVAL;
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}
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user = get_current_user();
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if (atomic_read(&user->fanotify_listeners) > FANOTIFY_DEFAULT_MAX_LISTENERS) {
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free_uid(user);
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