[PATCH bpf v2 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[PATCH bpf v2 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[Eugene Syromiatnikov]

Check that size would not overflow before calculation (and return
-EOVERFLOW if it will), to prevent potential out-of-bounds write
with the following copy_from_user.  Add the same check
to kprobe_multi_resolve_syms in case it will be called from elsewhere
in the future.

Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
 kernel/trace/bpf_trace.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d8553f4..f1d4e68 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2352,12 +2352,15 @@ static int
 kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
 			  unsigned long *addrs)
 {
-	unsigned long addr, size;
+	unsigned long addr, sym_size;
+	u32 size;
 	const char __user **syms;
 	int err = -ENOMEM;
 	unsigned int i;
 	char *func;
 
+	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
+		return -EOVERFLOW;
 	size = cnt * sizeof(*syms);
 	syms = kvzalloc(size, GFP_KERNEL);
 	if (!syms)
@@ -2382,9 +2385,9 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
 		addr = kallsyms_lookup_name(func);
 		if (!addr)
 			goto error;
-		if (!kallsyms_lookup_size_offset(addr, &size, NULL))
+		if (!kallsyms_lookup_size_offset(addr, &sym_size, NULL))
 			goto error;
-		addr = ftrace_location_range(addr, addr + size - 1);
+		addr = ftrace_location_range(addr, addr + sym_size - 1);
 		if (!addr)
 			goto error;
 		addrs[i] = addr;
@@ -2429,6 +2432,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (!cnt)
 		return -EINVAL;
 
+	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
+		return -EOVERFLOW;
 	size = cnt * sizeof(*addrs);
 	addrs = kvmalloc(size, GFP_KERNEL);
 	if (!addrs)
-- 
2.1.4

Re: [PATCH bpf v2 1/4] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[Yonghong Song]

On 5/16/22 4:04 PM, Eugene Syromiatnikov wrote:
> Check that size would not overflow before calculation (and return
> -EOVERFLOW if it will), to prevent potential out-of-bounds write
> with the following copy_from_user.  Add the same check
> to kprobe_multi_resolve_syms in case it will be called from elsewhere
> in the future.
> 
> Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
> Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
> ---
>   kernel/trace/bpf_trace.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d8553f4..f1d4e68 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2352,12 +2352,15 @@ static int
>   kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
>   			  unsigned long *addrs)
>   {
> -	unsigned long addr, size;
> +	unsigned long addr, sym_size;
> +	u32 size;
>   	const char __user **syms;
>   	int err = -ENOMEM;
>   	unsigned int i;
>   	char *func;
>   
> +	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
> +		return -EOVERFLOW;
>   	size = cnt * sizeof(*syms);

The statement 'size = cnt * sizeof(*syms)' can be removed right?
Here, the 'size' will be computed properly with check_mul_overflow()
if 0 is returned.

>   	syms = kvzalloc(size, GFP_KERNEL);
>   	if (!syms)
> @@ -2382,9 +2385,9 @@ kprobe_multi_resolve_syms(const void __user *usyms, u32 cnt,
>   		addr = kallsyms_lookup_name(func);
>   		if (!addr)
>   			goto error;
> -		if (!kallsyms_lookup_size_offset(addr, &size, NULL))
> +		if (!kallsyms_lookup_size_offset(addr, &sym_size, NULL))
>   			goto error;
> -		addr = ftrace_location_range(addr, addr + size - 1);
> +		addr = ftrace_location_range(addr, addr + sym_size - 1);
>   		if (!addr)
>   			goto error;
>   		addrs[i] = addr;
> @@ -2429,6 +2432,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>   	if (!cnt)
>   		return -EINVAL;
>   
> +	if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
> +		return -EOVERFLOW;
>   	size = cnt * sizeof(*addrs);

Same here, 'size = ...' is not needed.

>   	addrs = kvmalloc(size, GFP_KERNEL);
>   	if (!addrs)