From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Date: Wed, 10 Jan 2018 18:02:43 -0800 Message-Id: <1515636190-24061-12-git-send-email-keescook@chromium.org> In-Reply-To: <1515636190-24061-1-git-send-email-keescook@chromium.org> References: <1515636190-24061-1-git-send-email-keescook@chromium.org> Subject: [kernel-hardening] [PATCH 11/38] vfs: Define usercopy region in names_cache slab caches To: linux-kernel@vger.kernel.org Cc: Kees Cook , David Windsor , Alexander Viro , linux-fsdevel@vger.kernel.org, Linus Torvalds , Andrew Morton , Andy Lutomirski , Christoph Hellwig , Christoph Lameter , "David S. Miller" , Laura Abbott , Mark Rutland , "Martin K. Petersen" , Paolo Bonzini , Christian Borntraeger , Christoffer Dall , Dave Kleikamp , Jan Kara , Luis de Bethencourt , Marc Zyngier , Rik van Riel , Matthew Garrett , linux-arch@vger.kernel.org, netdev@vger.kernel.org, linux-mm@kvack.org, kernel-hardening@lists.openwall.com List-ID: From: David Windsor VFS pathnames are stored in the names_cache slab cache, either inline or across an entire allocation entry (when approaching PATH_MAX). These are copied to/from userspace, so they must be entirely whitelisted. cache object allocation: include/linux/fs.h: #define __getname() kmem_cache_alloc(names_cachep, GFP_KERNEL) example usage trace: strncpy_from_user+0x4d/0x170 getname_flags+0x6f/0x1f0 user_path_at_empty+0x23/0x40 do_mount+0x69/0xda0 SyS_mount+0x83/0xd0 fs/namei.c: getname_flags(...): ... result = __getname(); ... kname = (char *)result->iname; result->name = kname; len = strncpy_from_user(kname, filename, EMBEDDED_NAME_MAX); ... if (unlikely(len == EMBEDDED_NAME_MAX)) { const size_t size = offsetof(struct filename, iname[1]); kname = (char *)result; result = kzalloc(size, GFP_KERNEL); ... result->name = kname; len = strncpy_from_user(kname, filename, PATH_MAX); In support of usercopy hardening, this patch defines the entire cache object in the names_cache slab cache as whitelisted, since it may entirely hold name strings to be copied to/from userspace. This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY whitelisting code in the last public patch of grsecurity/PaX based on my understanding of the code. Changes or omissions from the original code are mine and don't reflect the original grsecurity/PaX code. Signed-off-by: David Windsor [kees: adjust commit log, add usage trace] Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Kees Cook --- fs/dcache.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 92ad7a2168e1..9d7ee2de682c 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3640,8 +3640,8 @@ void __init vfs_caches_init_early(void) void __init vfs_caches_init(void) { - names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0, - SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL); + names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0, + SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL); dcache_init(); inode_init(); -- 2.7.4