Date: Mon, 28 Aug 2017 14:57:14 -0700 From: Kees Cook <keescook@...omium.org> To: "Darrick J. Wong" <darrick.wong@...cle.com> Cc: LKML <linux-kernel@...r.kernel.org>, David Windsor <dave@...lcore.net>, linux-xfs@...r.kernel.org, Linux-MM <linux-mm@...ck.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH v2 15/30] xfs: Define usercopy region in xfs_inode slab cache On Mon, Aug 28, 2017 at 2:49 PM, Darrick J. Wong <darrick.wong@...cle.com> wrote: > On Mon, Aug 28, 2017 at 02:34:56PM -0700, Kees Cook wrote: >> From: David Windsor <dave@...lcore.net> >> >> The XFS inline inode data, stored in struct xfs_inode_t field >> i_df.if_u2.if_inline_data and therefore contained in the xfs_inode slab >> cache, needs to be copied to/from userspace. >> >> cache object allocation: >> fs/xfs/xfs_icache.c: >> xfs_inode_alloc(...): >> ... >> ip = kmem_zone_alloc(xfs_inode_zone, KM_SLEEP); >> >> fs/xfs/libxfs/xfs_inode_fork.c: >> xfs_init_local_fork(...): >> ... >> if (mem_size <= sizeof(ifp->if_u2.if_inline_data)) >> ifp->if_u1.if_data = ifp->if_u2.if_inline_data; > > Hmm, what happens when mem_size > sizeof(if_inline_data)? A slab object > will be allocated for ifp->if_u1.if_data which can then be used for > readlink in the same manner as the example usage trace below. Does > that allocated object have a need for a usercopy annotation like > the one we're adding for if_inline_data? Or is that already covered > elsewhere? Yeah, the xfs helper kmem_alloc() is used in the other case, which ultimately boils down to a call to kmalloc(), which is entirely whitelisted by an earlier patch in the series: https://lkml.org/lkml/2017/8/28/1026 (It's possible that at some future time we can start segregating kernel-only kmallocs from usercopy-able kmallocs, but for now, there are no plans for this.) -Kees -- Kees Cook Pixel Security
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