Messages in this thread | | | Date | Sat, 7 Mar 2009 10:27:35 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH -v2] memdup_user(): introduce |
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On Sat, 7 Mar 2009 08:48:05 -0800 Arjan van de Ven <arjan@infradead.org> wrote:
> On Fri, 6 Mar 2009 15:03:35 -0800 > Andrew Morton <akpm@linux-foundation.org> wrote: > > > > > > > /** > > > + * memdup_user - duplicate memory region from user space > > > + * > > > + * @src: source address in user space > > > + * @len: number of bytes to copy > > > + * @gfp: GFP mask to use > > > + * > > > + * Returns an ERR_PTR() on failure. > > > + */ > > > +void *memdup_user(const void __user *src, size_t len, gfp_t gfp) > > > +{ > > > + void *p; > > > + > > > + p = kmalloc_track_caller(len, gfp); > > > + if (!p) > > > + return ERR_PTR(-ENOMEM); > > > + > > > + if (copy_from_user(p, src, len)) { > > > + kfree(p); > > > + return ERR_PTR(-EFAULT); > > > + } > > > + > > > + return p; > > > +} > > > +EXPORT_SYMBOL(memdup_user); > > Hi, > > I like the general idea of this a lot; it will make things much less > error prone (and we can add some sanity checks on "len" to catch the > standard security holes around copy_from_user usage). I'd even also > want a memdup_array() like thing in the style of calloc(). > > However, I have two questions/suggestions for improvement: > > I would like to question the use of the gfp argument here; > copy_from_user sleeps, so you can't use GFP_ATOMIC anyway. > You can't use GFP_NOFS etc, because the pagefault path will happily do > things that are equivalent, if not identical, to GFP_KERNEL. > > So the only value you can pass in correctly, as far as I can see, is > GFP_KERNEL. Am I wrong?
True.
> A second thing.. I'd like to have this function return NULL on failure; > error checking a pointer for NULL is so much easier than testing for > anything else; the only distinction is -ENOMEM versus -EFAULT, and I'm > not sure that that is worth the complexity on all callers.
This errno will be returned to userspace. If the caller guesses wrong, that's a kernel bug, of the regression variety.
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