Messages in this thread | | | From | "Michael Kerrisk (man-pages)" <> | Date | Tue, 13 May 2014 10:25:14 +0200 | Subject | Re: [PATCH 1/1 v2] fanotify: check file flags passed in fanotify_init |
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Hello Heinrich
On Mon, May 12, 2014 at 9:02 PM, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote: > 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> > --- > fs/notify/fanotify/fanotify_user.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c > index d42220f..31b0de2 100644 > --- a/fs/notify/fanotify/fanotify_user.c > +++ b/fs/notify/fanotify/fanotify_user.c > @@ -25,6 +25,19 @@ > #define FANOTIFY_DEFAULT_MAX_MARKS 8192 > #define FANOTIFY_DEFAULT_MAX_LISTENERS 128 > > +/* > + * All flags that may be specified in parameter event_f_flags of fanotify_init. > + * > + * Internal and external open flags are stored together in field f_flags of > + * struct file. Only external open flags shall be allowed in event_f_flags. > + * Internal flags like FMODE_NONOTIFY, FMODE_EXEC, FMODE_NOCMTIME shall be > + * excluded. > + */ > +#define FANOTIFY_INIT_ALL_EVENT_F_BITS ( \ > + O_ACCMODE | O_APPEND | O_NONBLOCK | \ > + __O_SYNC | O_DSYNC | O_CLOEXEC | \ > + O_LARGEFILE | O_NOATIME ) > + > extern const struct fsnotify_ops fanotify_fsnotify_ops;
The above looks okay to me, but I'd be happier seeing an Ack from Jan or Eric.
> static struct kmem_cache *fanotify_mark_cache __read_mostly; > @@ -669,6 +682,18 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags) > if (flags & ~FAN_ALL_INIT_FLAGS) > return -EINVAL; > > + if (event_f_flags & ~FANOTIFY_INIT_ALL_EVENT_F_BITS) > + return -EINVAL; > + > + switch (event_f_flags & O_ACCMODE) { > + case O_RDONLY: > + case O_RDWR: > + case O_WRONLY: > + break; > + default: > + return -EINVAL; > + } > +
The 'switch' could just be replaced by:
if ((event_f_flags & O_ACCMODE) == 3) return -EINVAL;
(But I'm not sure if some might prefer the idiom you have used.)
Cheers,
Michael
-- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
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