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Mon, 04 Mar 2024 13:32:21 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id w62-20020a636241000000b005e485fbd455sm7872070pgb.45.2024.03.04.13.32.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Mar 2024 13:32:21 -0800 (PST) Date: Mon, 4 Mar 2024 13:32:20 -0800 From: Kees Cook To: Dave Chinner Cc: Vlastimil Babka , Christian Brauner , Alexander Viro , Jan Kara , linux-fsdevel@vger.kernel.org, "GONG, Ruiqi" , Xiu Jianfeng , Suren Baghdasaryan , Kent Overstreet , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 3/4] xattr: Use dedicated slab buckets for setxattr() Message-ID: <202403041330.06842D397@keescook> References: <20240304184252.work.496-kees@kernel.org> <20240304184933.3672759-3-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C822E40023 X-Stat-Signature: q78jbxnzyd7jh8et7y1hinbgsd6enazw X-Rspam-User: X-HE-Tag: 1709587942-371414 X-HE-Meta: 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 bKNV+LJz 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 05, 2024 at 08:16:30AM +1100, Dave Chinner wrote: > On Mon, Mar 04, 2024 at 10:49:31AM -0800, Kees Cook wrote: > > The setxattr() API can be used for exploiting[1][2][3] use-after-free > > type confusion flaws in the kernel. Avoid having a user-controlled size > > cache share the global kmalloc allocator by using a separate set of > > kmalloc buckets. > > > > Link: https://duasynt.com/blog/linux-kernel-heap-spray [1] > > Link: https://etenal.me/archives/1336 [2] > > Link: https://github.com/a13xp0p0v/kernel-hack-drill/blob/master/drill_exploit_uaf.c [3] > > Signed-off-by: Kees Cook > > --- > > Cc: Christian Brauner > > Cc: Alexander Viro > > Cc: Jan Kara > > Cc: linux-fsdevel@vger.kernel.org > > --- > > fs/xattr.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/fs/xattr.c b/fs/xattr.c > > index 09d927603433..2b06316f1d1f 100644 > > --- a/fs/xattr.c > > +++ b/fs/xattr.c > > @@ -821,6 +821,16 @@ SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name, > > return error; > > } > > > > +static struct kmem_buckets *xattr_buckets; > > +static int __init init_xattr_buckets(void) > > +{ > > + xattr_buckets = kmem_buckets_create("xattr", 0, 0, 0, > > + XATTR_LIST_MAX, NULL); > > + > > + return 0; > > +} > > +subsys_initcall(init_xattr_buckets); > > + > > /* > > * Extended attribute LIST operations > > */ > > @@ -833,7 +843,7 @@ listxattr(struct dentry *d, char __user *list, size_t size) > > if (size) { > > if (size > XATTR_LIST_MAX) > > size = XATTR_LIST_MAX; > > - klist = kvmalloc(size, GFP_KERNEL); > > + klist = kmem_buckets_alloc(xattr_buckets, size, GFP_KERNEL); > > There's a reason this uses kvmalloc() - allocations can be up to > 64kB in size and it's not uncommon for large slab allocation to > fail on long running machines. hence this needs to fall back to > vmalloc() to ensure that large xattrs can always be read. I can add a vmalloc fallback interface too. It looked like the larger xattr usage (8k-64k) was less common, but yeah, let's not remove the correct allocation fallback here. I'll fix this for v2. Thanks! -Kees -- Kees Cook