Messages in this thread | | | Date | Tue, 29 Mar 2022 13:20:11 +0200 | From | Christian Brauner <> | Subject | Re: [PATCH] binderfs: Fix the maximum minor value in binderfs_binder_device_create() and binderfs_binder_ctl_create() |
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On Sun, Mar 27, 2022 at 01:18:17PM +0200, Christophe JAILLET wrote: > ida_alloc_max(..., max, ...) returns values from 0 to max, inclusive. > > So, BINDERFS_MAX_MINOR is a valid value for 'minor'. > > BINDERFS_MAX_MINOR is '1U << MINORBITS' and we have: > #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi)) > > So, When this value is used in MKDEV() and it will overflow. > > Fixes: 3ad20fe393b3 ("binder: implement binderfs") > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > --- > This patch is completely speculative. > > The 'BINDERFS_MAX_MINOR_CAPPED - 1' is here only for symmetry with the > BINDERFS_MAX_MINOR case. I'm not sure at all that is is needed and, more > importantly, that it is correct.
Hm, since we're "removing" one alloctable device for the initial ipc namespace, I think we need the -1 for the capped value.
Though I wonder if the simpler fix wouldn't just be to:
#define BINDERFS_MAX_MINOR MINORMASK
since include/linux/kdev_t.h has:
#define MINORBITS 20 #define MINORMASK ((1U << MINORBITS) - 1)
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