Re: [PATCH] netfilter: add overflow checks in xt_bpf.c
On Fri, Dec 01, 2017 at 01:46:07AM +0100, Jann Horn wrote: > Check whether inputs from userspace are too long (explicit length field too > big or string not null-terminated) to avoid out-of-bounds reads. > > As far as I can tell, this can at worst lead to very limited kernel heap > memory disclosure or oopses. > > This bug can be triggered by an unprivileged user even if the xt_bpf module > is not loaded: iptables is available in network namespaces, and the xt_bpf > module can be autoloaded. > > Triggering the bug with a classic BPF filter with fake length 0x1000 causes > the following KASAN report: > > == > BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0 > Read of size 32768 at addr 8801eff2c494 by task test/4627 > > CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1 > [...] > Call Trace: > dump_stack+0x5c/0x85 > print_address_description+0x6a/0x260 > kasan_report+0x254/0x370 > ? bpf_prog_create+0x84/0xf0 > memcpy+0x1f/0x50 > bpf_prog_create+0x84/0xf0 > bpf_mt_check+0x90/0xd6 [xt_bpf] > [...] > Allocated by task 4627: > kasan_kmalloc+0xa0/0xd0 > __kmalloc_node+0x47/0x60 > xt_alloc_table_info+0x41/0x70 [x_tables] > [...] > The buggy address belongs to the object at 8801eff2c3c0 > which belongs to the cache kmalloc-2048 of size 2048 > The buggy address is located 212 bytes inside of > 2048-byte region [8801eff2c3c0, 8801eff2cbc0) > [...] > == Applied, thanks.
Re: [PATCH] netfilter: add overflow checks in xt_bpf.c
On Thu, Nov 30, 2017 at 11:08 PM, Jann Hornwrote: > On Fri, Dec 1, 2017 at 5:04 AM, Willem de Bruijn > wrote: >> On Thu, Nov 30, 2017 at 7:46 PM, Jann Horn wrote: >>> Check whether inputs from userspace are too long (explicit length field too >>> big or string not null-terminated) to avoid out-of-bounds reads. >>> >>> As far as I can tell, this can at worst lead to very limited kernel heap >>> memory disclosure or oopses. >>> >>> This bug can be triggered by an unprivileged user even if the xt_bpf module >>> is not loaded: iptables is available in network namespaces, and the xt_bpf >>> module can be autoloaded. >>> >>> Triggering the bug with a classic BPF filter with fake length 0x1000 causes >>> the following KASAN report: >>> >>> == >>> BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0 >>> Read of size 32768 at addr 8801eff2c494 by task test/4627 >>> >>> CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1 >>> [...] >>> Call Trace: >>> dump_stack+0x5c/0x85 >>> print_address_description+0x6a/0x260 >>> kasan_report+0x254/0x370 >>> ? bpf_prog_create+0x84/0xf0 >>> memcpy+0x1f/0x50 >>> bpf_prog_create+0x84/0xf0 >>> bpf_mt_check+0x90/0xd6 [xt_bpf] >>> [...] >>> Allocated by task 4627: >>> kasan_kmalloc+0xa0/0xd0 >>> __kmalloc_node+0x47/0x60 >>> xt_alloc_table_info+0x41/0x70 [x_tables] >>> [...] >>> The buggy address belongs to the object at 8801eff2c3c0 >>> which belongs to the cache kmalloc-2048 of size 2048 >>> The buggy address is located 212 bytes inside of >>> 2048-byte region [8801eff2c3c0, 8801eff2cbc0) >>> [...] >>> == >>> >>> Fixes: e6f30c731718 ("netfilter: x_tables: add xt_bpf match") >>> Signed-off-by: Jann Horn >>> --- >>> net/netfilter/xt_bpf.c | 6 ++ >>> 1 file changed, 6 insertions(+) >>> >>> diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c >>> index 041da0d9c06f..1f7fbd3c7e5a 100644 >>> --- a/net/netfilter/xt_bpf.c >>> +++ b/net/netfilter/xt_bpf.c >>> @@ -27,6 +27,9 @@ static int __bpf_mt_check_bytecode(struct sock_filter >>> *insns, __u16 len, >>> { >>> struct sock_fprog_kern program; >>> >>> + if (len > XT_BPF_MAX_NUM_INSTR) >>> + return -EINVAL; >>> + >>> program.len = len; >>> program.filter = insns; >> >> Next, this calls bpf_prog_create, which calls bpf_check_basics_ok to verify >> len. > > Irrelevant: > > - see the KASAN splat in the commit message > - bpf_check_basics_ok checks against BPF_MAXINSNS (4096), but a check against >XT_BPF_MAX_NUM_INSTR (64) is needed because that's the size of the > member in the >input struct Argh, of course. Thanks.
Re: [PATCH] netfilter: add overflow checks in xt_bpf.c
On Fri, Dec 1, 2017 at 5:04 AM, Willem de Bruijnwrote: > On Thu, Nov 30, 2017 at 7:46 PM, Jann Horn wrote: >> Check whether inputs from userspace are too long (explicit length field too >> big or string not null-terminated) to avoid out-of-bounds reads. >> >> As far as I can tell, this can at worst lead to very limited kernel heap >> memory disclosure or oopses. >> >> This bug can be triggered by an unprivileged user even if the xt_bpf module >> is not loaded: iptables is available in network namespaces, and the xt_bpf >> module can be autoloaded. >> >> Triggering the bug with a classic BPF filter with fake length 0x1000 causes >> the following KASAN report: >> >> == >> BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0 >> Read of size 32768 at addr 8801eff2c494 by task test/4627 >> >> CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1 >> [...] >> Call Trace: >> dump_stack+0x5c/0x85 >> print_address_description+0x6a/0x260 >> kasan_report+0x254/0x370 >> ? bpf_prog_create+0x84/0xf0 >> memcpy+0x1f/0x50 >> bpf_prog_create+0x84/0xf0 >> bpf_mt_check+0x90/0xd6 [xt_bpf] >> [...] >> Allocated by task 4627: >> kasan_kmalloc+0xa0/0xd0 >> __kmalloc_node+0x47/0x60 >> xt_alloc_table_info+0x41/0x70 [x_tables] >> [...] >> The buggy address belongs to the object at 8801eff2c3c0 >> which belongs to the cache kmalloc-2048 of size 2048 >> The buggy address is located 212 bytes inside of >> 2048-byte region [8801eff2c3c0, 8801eff2cbc0) >> [...] >> == >> >> Fixes: e6f30c731718 ("netfilter: x_tables: add xt_bpf match") >> Signed-off-by: Jann Horn >> --- >> net/netfilter/xt_bpf.c | 6 ++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c >> index 041da0d9c06f..1f7fbd3c7e5a 100644 >> --- a/net/netfilter/xt_bpf.c >> +++ b/net/netfilter/xt_bpf.c >> @@ -27,6 +27,9 @@ static int __bpf_mt_check_bytecode(struct sock_filter >> *insns, __u16 len, >> { >> struct sock_fprog_kern program; >> >> + if (len > XT_BPF_MAX_NUM_INSTR) >> + return -EINVAL; >> + >> program.len = len; >> program.filter = insns; > > Next, this calls bpf_prog_create, which calls bpf_check_basics_ok to verify > len. Irrelevant: - see the KASAN splat in the commit message - bpf_check_basics_ok checks against BPF_MAXINSNS (4096), but a check against XT_BPF_MAX_NUM_INSTR (64) is needed because that's the size of the member in the input struct
Re: [PATCH] netfilter: add overflow checks in xt_bpf.c
On Thu, Nov 30, 2017 at 7:46 PM, Jann Hornwrote: > Check whether inputs from userspace are too long (explicit length field too > big or string not null-terminated) to avoid out-of-bounds reads. > > As far as I can tell, this can at worst lead to very limited kernel heap > memory disclosure or oopses. > > This bug can be triggered by an unprivileged user even if the xt_bpf module > is not loaded: iptables is available in network namespaces, and the xt_bpf > module can be autoloaded. > > Triggering the bug with a classic BPF filter with fake length 0x1000 causes > the following KASAN report: > > == > BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0 > Read of size 32768 at addr 8801eff2c494 by task test/4627 > > CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1 > [...] > Call Trace: > dump_stack+0x5c/0x85 > print_address_description+0x6a/0x260 > kasan_report+0x254/0x370 > ? bpf_prog_create+0x84/0xf0 > memcpy+0x1f/0x50 > bpf_prog_create+0x84/0xf0 > bpf_mt_check+0x90/0xd6 [xt_bpf] > [...] > Allocated by task 4627: > kasan_kmalloc+0xa0/0xd0 > __kmalloc_node+0x47/0x60 > xt_alloc_table_info+0x41/0x70 [x_tables] > [...] > The buggy address belongs to the object at 8801eff2c3c0 > which belongs to the cache kmalloc-2048 of size 2048 > The buggy address is located 212 bytes inside of > 2048-byte region [8801eff2c3c0, 8801eff2cbc0) > [...] > == > > Fixes: e6f30c731718 ("netfilter: x_tables: add xt_bpf match") > Signed-off-by: Jann Horn > --- > net/netfilter/xt_bpf.c | 6 ++ > 1 file changed, 6 insertions(+) > > diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c > index 041da0d9c06f..1f7fbd3c7e5a 100644 > --- a/net/netfilter/xt_bpf.c > +++ b/net/netfilter/xt_bpf.c > @@ -27,6 +27,9 @@ static int __bpf_mt_check_bytecode(struct sock_filter > *insns, __u16 len, > { > struct sock_fprog_kern program; > > + if (len > XT_BPF_MAX_NUM_INSTR) > + return -EINVAL; > + > program.len = len; > program.filter = insns; Next, this calls bpf_prog_create, which calls bpf_check_basics_ok to verify len. > @@ -55,6 +58,9 @@ static int __bpf_mt_check_path(const char *path, struct > bpf_prog **ret) > mm_segment_t oldfs = get_fs(); > int retval, fd; > > + if (strnlen(path, XT_BPF_PATH_MAX) == XT_BPF_PATH_MAX) > + return -EINVAL; > + Good catch. It looks like this code needs a more thorough revision. https://lkml.kernel.org/r/<20171201034859.gn21...@zeniv.linux.org.uk>