From fbca9d2d35c6ef1b323fae75cc9545005ba25097 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 30 Nov 2015 13:02:56 +0100 Subject: bpf, array: fix heap out-of-bounds access when updating elements During own review but also reported by Dmitry's syzkaller [1] it has been noticed that we trigger a heap out-of-bounds access on eBPF array maps when updating elements. This happens with each map whose map->value_size (specified during map creation time) is not multiple of 8 bytes. In array_map_alloc(), elem_size is round_up(attr->value_size, 8) and used to align array map slots for faster access. However, in function array_map_update_elem(), we update the element as ... memcpy(array->value + array->elem_size * index, value, array->elem_size); ... where we access 'value' out-of-bounds, since it was allocated from map_update_elem() from syscall side as kmalloc(map->value_size, GFP_USER) and later on copied through copy_from_user(value, uvalue, map->value_size). Thus, up to 7 bytes, we can access out-of-bounds. Same could happen from within an eBPF program, where in worst case we access beyond an eBPF program's designated stack. Since 1be7f75d1668 ("bpf: enable non-root eBPF programs") didn't hit an official release yet, it only affects priviledged users. In case of array_map_lookup_elem(), the verifier prevents eBPF programs from accessing beyond map->value_size through check_map_access(). Also from syscall side map_lookup_elem() only copies map->value_size back to user, so nothing could leak. [1] http://github.com/google/syzkaller Fixes: 28fbcfa08d8e ("bpf: add array type of eBPF maps") Reported-by: Dmitry Vyukov Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- kernel/bpf/arraymap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/bpf/arraymap.c') diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index 3f4c99e06c6b..4c67ce39732e 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -105,7 +105,7 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value, /* all elements already exist */ return -EEXIST; - memcpy(array->value + array->elem_size * index, value, array->elem_size); + memcpy(array->value + array->elem_size * index, value, map->value_size); return 0; } -- cgit From 01b3f52157ff5a47d6d8d796f396a4b34a53c61d Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Sun, 29 Nov 2015 16:59:35 -0800 Subject: bpf: fix allocation warnings in bpf maps and integer overflow For large map->value_size the user space can trigger memory allocation warnings like: WARNING: CPU: 2 PID: 11122 at mm/page_alloc.c:2989 __alloc_pages_nodemask+0x695/0x14e0() Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [] dump_stack+0x68/0x92 lib/dump_stack.c:50 [] warn_slowpath_common+0xd9/0x140 kernel/panic.c:460 [] warn_slowpath_null+0x29/0x30 kernel/panic.c:493 [< inline >] __alloc_pages_slowpath mm/page_alloc.c:2989 [] __alloc_pages_nodemask+0x695/0x14e0 mm/page_alloc.c:3235 [] alloc_pages_current+0xee/0x340 mm/mempolicy.c:2055 [< inline >] alloc_pages include/linux/gfp.h:451 [] alloc_kmem_pages+0x16/0xf0 mm/page_alloc.c:3414 [] kmalloc_order+0x19/0x60 mm/slab_common.c:1007 [] kmalloc_order_trace+0x1f/0xa0 mm/slab_common.c:1018 [< inline >] kmalloc_large include/linux/slab.h:390 [] __kmalloc+0x234/0x250 mm/slub.c:3525 [< inline >] kmalloc include/linux/slab.h:463 [< inline >] map_update_elem kernel/bpf/syscall.c:288 [< inline >] SYSC_bpf kernel/bpf/syscall.c:744 To avoid never succeeding kmalloc with order >= MAX_ORDER check that elem->value_size and computed elem_size are within limits for both hash and array type maps. Also add __GFP_NOWARN to kmalloc(value_size | elem_size) to avoid OOM warnings. Note kmalloc(key_size) is highly unlikely to trigger OOM, since key_size <= 512, so keep those kmalloc-s as-is. Large value_size can cause integer overflows in elem_size and map.pages formulas, so check for that as well. Fixes: aaac3ba95e4c ("bpf: charge user for creation of BPF maps and programs") Reported-by: Dmitry Vyukov Signed-off-by: Alexei Starovoitov Signed-off-by: David S. Miller --- kernel/bpf/arraymap.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'kernel/bpf/arraymap.c') diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index 4c67ce39732e..b0799bced518 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -28,11 +28,17 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr) attr->value_size == 0) return ERR_PTR(-EINVAL); + if (attr->value_size >= 1 << (KMALLOC_SHIFT_MAX - 1)) + /* if value_size is bigger, the user space won't be able to + * access the elements. + */ + return ERR_PTR(-E2BIG); + elem_size = round_up(attr->value_size, 8); /* check round_up into zero and u32 overflow */ if (elem_size == 0 || - attr->max_entries > (U32_MAX - sizeof(*array)) / elem_size) + attr->max_entries > (U32_MAX - PAGE_SIZE - sizeof(*array)) / elem_size) return ERR_PTR(-ENOMEM); array_size = sizeof(*array) + attr->max_entries * elem_size; -- cgit