[PATCH] bpf: Use safer kvmalloc_array() where possible

[PATCH] bpf: Use safer kvmalloc_array() where possible

[Dan Carpenter]

The kvmalloc_array() function is safer because it has a check for
integer overflows.  These sizes come from the user and I was not
able to see any bounds checking so an integer overflow seems like a
realistic concern.

Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 kernel/trace/bpf_trace.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 10b157a6d73e..7a13e6ac6327 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2263,11 +2263,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
 	int err = -ENOMEM;
 	unsigned int i;
 
-	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
+	syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
 	if (!syms)
 		goto error;
 
-	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
+	buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
 	if (!buf)
 		goto error;
 
@@ -2464,7 +2464,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 		return -EINVAL;
 
 	size = cnt * sizeof(*addrs);
-	addrs = kvmalloc(size, GFP_KERNEL);
+	addrs = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
 	if (!addrs)
 		return -ENOMEM;
 
@@ -2489,7 +2489,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 
 	ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
 	if (ucookies) {
-		cookies = kvmalloc(size, GFP_KERNEL);
+		cookies = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
 		if (!cookies) {
 			err = -ENOMEM;
 			goto error;
-- 
2.35.1

Re: [PATCH] bpf: Use safer kvmalloc_array() where possible

[Yonghong Song]

On 5/26/22 3:24 AM, Dan Carpenter wrote:
> The kvmalloc_array() function is safer because it has a check for
> integer overflows.  These sizes come from the user and I was not
> able to see any bounds checking so an integer overflow seems like a
> realistic concern.
> 
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>   kernel/trace/bpf_trace.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 10b157a6d73e..7a13e6ac6327 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2263,11 +2263,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
>   	int err = -ENOMEM;
>   	unsigned int i;
>   
> -	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> +	syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
>   	if (!syms)
>   		goto error;
>   
> -	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> +	buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
>   	if (!buf)
>   		goto error;
>   
> @@ -2464,7 +2464,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr

For this part of change, there is a similar pending patch here:
https://lore.kernel.org/bpf/399e634781822329e856103cddba975f58f0498c.1652982525.git.esyr@redhat.com/
which waits for further review. That patch tries to detect the overflow
explicitly to avoid possible kernel dmesg warnings. (See function 
kvmalloc_node()).

>   		return -EINVAL;
>   
>   	size = cnt * sizeof(*addrs);
> -	addrs = kvmalloc(size, GFP_KERNEL);
> +	addrs = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
>   	if (!addrs)
>   		return -ENOMEM;
>   
> @@ -2489,7 +2489,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>   
>   	ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
>   	if (ucookies) {
> -		cookies = kvmalloc(size, GFP_KERNEL);
> +		cookies = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
>   		if (!cookies) {
>   			err = -ENOMEM;
>   			goto error;

Re: [PATCH] bpf: Use safer kvmalloc_array() where possible

[Jiri Olsa]

On Thu, May 26, 2022 at 01:24:05PM +0300, Dan Carpenter wrote:
> The kvmalloc_array() function is safer because it has a check for
> integer overflows.  These sizes come from the user and I was not
> able to see any bounds checking so an integer overflow seems like a
> realistic concern.
> 
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Eugene was addressing these:
  https://lore.kernel.org/bpf/399e634781822329e856103cddba975f58f0498c.1652982525.git.esyr@redhat.com/

I think using kvmalloc_array was one of the review comments

jirka


> ---
>  kernel/trace/bpf_trace.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 10b157a6d73e..7a13e6ac6327 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2263,11 +2263,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
>  	int err = -ENOMEM;
>  	unsigned int i;
>  
> -	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> +	syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
>  	if (!syms)
>  		goto error;
>  
> -	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> +	buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
>  	if (!buf)
>  		goto error;
>  
> @@ -2464,7 +2464,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>  		return -EINVAL;
>  
>  	size = cnt * sizeof(*addrs);
> -	addrs = kvmalloc(size, GFP_KERNEL);
> +	addrs = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
>  	if (!addrs)
>  		return -ENOMEM;
>  
> @@ -2489,7 +2489,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>  
>  	ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
>  	if (ucookies) {
> -		cookies = kvmalloc(size, GFP_KERNEL);
> +		cookies = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
>  		if (!cookies) {
>  			err = -ENOMEM;
>  			goto error;
> -- 
> 2.35.1
> 

Re: [PATCH] bpf: Use safer kvmalloc_array() where possible

[Dan Carpenter]

On Thu, May 26, 2022 at 08:31:10AM -0700, Yonghong Song wrote:
> 
> 
> On 5/26/22 3:24 AM, Dan Carpenter wrote:
> > The kvmalloc_array() function is safer because it has a check for
> > integer overflows.  These sizes come from the user and I was not
> > able to see any bounds checking so an integer overflow seems like a
> > realistic concern.
> > 
> > Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> >   kernel/trace/bpf_trace.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 10b157a6d73e..7a13e6ac6327 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -2263,11 +2263,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
> >   	int err = -ENOMEM;
> >   	unsigned int i;
> > -	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> > +	syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
> >   	if (!syms)
> >   		goto error;
> > -	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> > +	buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
> >   	if (!buf)
> >   		goto error;
> > @@ -2464,7 +2464,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> 
> For this part of change, there is a similar pending patch here:
> https://lore.kernel.org/bpf/399e634781822329e856103cddba975f58f0498c.1652982525.git.esyr@redhat.com/
> which waits for further review. That patch tries to detect the overflow
> explicitly to avoid possible kernel dmesg warnings. (See function
> kvmalloc_node()).

That patch doesn't apply any more.

Static checkers will insist that kvmalloc_array() is cleaner and safer
than kvmalloc(n * size, and they don't care if the integer overflow is
real or not.

-EOVERFLOW is the wrong error code.  Just return -ENOMEM.  Checking for
size > INT_MAX is ugly.  Use a correct limit based on what the maximum
reasonable size is.  Or if we only want to prevent the stack dump then
just pass __GFP_NOWARN.

It annoyed me that size was type unsigned int.  Sizes should be unsigned
long.  Every alloc() function takes an unsigned long so using a u32
temporary value for the size is what made this code so dangerous.  If
it had been:

	addrs = kvmalloc(cnt * sizeof(*addrs), GFP_KERNEL);

instead of:

	size = cnt * sizeof(*addrs);
	addrs = kvmalloc(size, GFP_KERNEL);

Then the integer overflow bug would only have affected 32 bit systems
and those are pretty rare.  Choosing the wrong type took a minor bug and
made it affect everyone.

regards,
dan carpenter

Re: [PATCH] bpf: Use safer kvmalloc_array() where possible

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Thu, 26 May 2022 13:24:05 +0300 you wrote:
> The kvmalloc_array() function is safer because it has a check for
> integer overflows.  These sizes come from the user and I was not
> able to see any bounds checking so an integer overflow seems like a
> realistic concern.
> 
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> [...]

Here is the summary with links:
  - bpf: Use safer kvmalloc_array() where possible
    https://git.kernel.org/bpf/bpf-next/c/dafd0f870eae

You are awesome, thank you!
-- 
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