[PATCH -next] libbpf: Add additional null-pointer checking in make_parent_dir

[PATCH -next] libbpf: Add additional null-pointer checking in make_parent_dir

[Gaosheng Cui]

The make_parent_dir is called without null-pointer checking for path,
such as bpf_link__pin. To ensure there is no null-pointer dereference
in make_parent_dir, so make_parent_dir requires additional null-pointer
checking for path.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
---
 tools/lib/bpf/libbpf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b53e51884f9e..5786e6184bf5 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7634,6 +7634,9 @@ static int make_parent_dir(const char *path)
 	char *dname, *dir;
 	int err = 0;
 
+	if (path == NULL)
+		return -EINVAL;
+
 	dname = strdup(path);
 	if (dname == NULL)
 		return -ENOMEM;
-- 
2.25.1

Re: [PATCH -next] libbpf: Add additional null-pointer checking in make_parent_dir

[Andrii Nakryiko]

On Thu, Apr 21, 2022 at 6:01 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
>
> The make_parent_dir is called without null-pointer checking for path,
> such as bpf_link__pin. To ensure there is no null-pointer dereference
> in make_parent_dir, so make_parent_dir requires additional null-pointer
> checking for path.
>
> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
> ---
>  tools/lib/bpf/libbpf.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b53e51884f9e..5786e6184bf5 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7634,6 +7634,9 @@ static int make_parent_dir(const char *path)
>         char *dname, *dir;
>         int err = 0;
>
> +       if (path == NULL)
> +               return -EINVAL;
> +

API contract is that path shouldn't be NULL. Just like we don't check
link, obj, prog for NULL in every single API, I don't think we need to
do it here, unless I'm missing something?

>         dname = strdup(path);
>         if (dname == NULL)
>                 return -ENOMEM;
> --
> 2.25.1
>

Re: [PATCH -next] libbpf: Add additional null-pointer checking in make_parent_dir

[cuigaosheng]

I don't understand why we don't check path for NULL, bpf_link__pin is an external
interface, It will be called by external functions and provide input parameters,
for example in samples/bpf/hbm.c:
> 201 link = bpf_program__attach_cgroup(bpf_prog, cg1); 202 if 
> (libbpf_get_error(link)) { 203 fprintf(stderr, "ERROR: 
> bpf_program__attach_cgroup failed\n"); 204 goto err; 205 } 206 207 
> sprintf(cg_pin_path, "/sys/fs/bpf/hbm%d", cg_id); 208 rc = 
> bpf_link__pin(link, cg_pin_path); 209 if (rc < 0) { 210 printf("ERROR: 
> bpf_link__pin failed: %d\n", rc); 211 goto err; 212 }
if cg_pin_path is NULL, strdup(NULL) will trigger a segmentation fault in
make_parent_dir, I think we should avoid this and add null-pointer checking
for path, just like check_path:
> 7673 static int check_path(const char *path) 7674 { 7675 char *cp, 
> errmsg[STRERR_BUFSIZE]; 7676 struct statfs st_fs; 7677 char *dname, 
> *dir; 7678 int err = 0; 7679 7680 if (path == NULL) 7681 return 
> -EINVAL; 7682 7683 dname = strdup(path); 7684 if (dname == NULL) 7685 
> return -ENOMEM; 7686 7687 dir = dirname(dname); 7688 if (statfs(dir, 
> &st_fs)) { 7689 cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg)); 
> 7690 pr_warn("failed to statfs %s: %s\n", dir, cp); 7691 err = -errno; 
> 7692 } 7693 free(dname); 7694 7695 if (!err && st_fs.f_type != 
> BPF_FS_MAGIC) { 7696 pr_warn("specified path %s is not on BPF FS\n", 
> path); 7697 err = -EINVAL; 7698 } 7699 7700 return err; 7701 }

Thanks.

在 2022/4/22 0:55, Andrii Nakryiko 写道:
> On Thu, Apr 21, 2022 at 6:01 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
>> The make_parent_dir is called without null-pointer checking for path,
>> such as bpf_link__pin. To ensure there is no null-pointer dereference
>> in make_parent_dir, so make_parent_dir requires additional null-pointer
>> checking for path.
>>
>> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index b53e51884f9e..5786e6184bf5 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7634,6 +7634,9 @@ static int make_parent_dir(const char *path)
>>          char *dname, *dir;
>>          int err = 0;
>>
>> +       if (path == NULL)
>> +               return -EINVAL;
>> +
> API contract is that path shouldn't be NULL. Just like we don't check
> link, obj, prog for NULL in every single API, I don't think we need to
> do it here, unless I'm missing something?
>
>>          dname = strdup(path);
>>          if (dname == NULL)
>>                  return -ENOMEM;
>> --
>> 2.25.1
>>
> .

Re: [PATCH -next] libbpf: Add additional null-pointer checking in make_parent_dir

[cuigaosheng]

This email adjusts the code format.

I don't understand why we don't check path for NULL, bpf_link__pin is an 
external
interface, It will be called by external functions and provide input 
parameters,
for example in samples/bpf/hbm.c:

> 201         link = bpf_program__attach_cgroup(bpf_prog, cg1);
> 202         if (libbpf_get_error(link)) {
> 203                 fprintf(stderr, "ERROR: bpf_program__attach_cgroup 
> failed\n");
> 204                 goto err;
> 205         }
> 206
> 207         sprintf(cg_pin_path, "/sys/fs/bpf/hbm%d", cg_id);
> 208         rc = bpf_link__pin(link, cg_pin_path);
> 209         if (rc < 0) {
> 210                 printf("ERROR: bpf_link__pin failed: %d\n", rc);
> 211                 goto err;
> 212         }

if cg_pin_path is NULL, strdup(NULL) will trigger a segmentation fault in
make_parent_dir, I think we should avoid this and add null-pointer checking
for path, just like check_path:
>  7673 static int check_path(const char *path)
>  7674 {
>  7675         char *cp, errmsg[STRERR_BUFSIZE];
>  7676         struct statfs st_fs;
>  7677         char *dname, *dir;
>  7678         int err = 0;
>  7679
>  7680         if (path == NULL)
>  7681                 return -EINVAL;
>  7682
>  7683         dname = strdup(path);
>  7684         if (dname == NULL)
>  7685                 return -ENOMEM;
>  7686
>  7687         dir = dirname(dname);
>  7688         if (statfs(dir, &st_fs)) {
>  7689                 cp = libbpf_strerror_r(errno, errmsg, 
> sizeof(errmsg));
>  7690                 pr_warn("failed to statfs %s: %s\n", dir, cp);
>  7691                 err = -errno;
>  7692         }
>  7693         free(dname);
>  7694
>  7695         if (!err && st_fs.f_type != BPF_FS_MAGIC) {
>  7696                 pr_warn("specified path %s is not on BPF FS\n", 
> path);
>  7697                 err = -EINVAL;
>  7698         }
>  7699
>  7700         return err;
>  7701 }

Thanks.


在 2022/4/22 0:55, Andrii Nakryiko 写道:
> On Thu, Apr 21, 2022 at 6:01 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
>> The make_parent_dir is called without null-pointer checking for path,
>> such as bpf_link__pin. To ensure there is no null-pointer dereference
>> in make_parent_dir, so make_parent_dir requires additional null-pointer
>> checking for path.
>>
>> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
>> ---
>>   tools/lib/bpf/libbpf.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index b53e51884f9e..5786e6184bf5 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7634,6 +7634,9 @@ static int make_parent_dir(const char *path)
>>          char *dname, *dir;
>>          int err = 0;
>>
>> +       if (path == NULL)
>> +               return -EINVAL;
>> +
> API contract is that path shouldn't be NULL. Just like we don't check
> link, obj, prog for NULL in every single API, I don't think we need to
> do it here, unless I'm missing something?
>
>>          dname = strdup(path);
>>          if (dname == NULL)
>>                  return -ENOMEM;
>> --
>> 2.25.1
>>
> .

Re: [PATCH -next] libbpf: Add additional null-pointer checking in make_parent_dir

[Andrii Nakryiko]

On Thu, Apr 21, 2022 at 7:55 PM cuigaosheng <cuigaosheng1@huawei.com> wrote:
>
> This email adjusts the code format.
>
> I don't understand why we don't check path for NULL, bpf_link__pin is an
> external
> interface, It will be called by external functions and provide input
> parameters,

that external interface expects non-NULL string as input argument,
which is a default throughout libbpf's API. You will get SIGSEGV in
lots of cases if you pass NULL where you are not supposed to, e.g.,
bpf_object__open_file() and many others. It doesn't mean that libbpf
should check any pointer argument for NULL.

You can argue that strdup(NULL) shouldn't crash but it doesn't. It's
because strdup() has a contract that it shouldn't be passed NULL. So
is the case here.


> for example in samples/bpf/hbm.c:
>
> > 201         link = bpf_program__attach_cgroup(bpf_prog, cg1);
> > 202         if (libbpf_get_error(link)) {
> > 203                 fprintf(stderr, "ERROR: bpf_program__attach_cgroup
> > failed\n");
> > 204                 goto err;
> > 205         }
> > 206
> > 207         sprintf(cg_pin_path, "/sys/fs/bpf/hbm%d", cg_id);
> > 208         rc = bpf_link__pin(link, cg_pin_path);
> > 209         if (rc < 0) {
> > 210                 printf("ERROR: bpf_link__pin failed: %d\n", rc);
> > 211                 goto err;
> > 212         }
>
> if cg_pin_path is NULL, strdup(NULL) will trigger a segmentation fault in
> make_parent_dir, I think we should avoid this and add null-pointer checking
> for path, just like check_path:
> >  7673 static int check_path(const char *path)
> >  7674 {
> >  7675         char *cp, errmsg[STRERR_BUFSIZE];
> >  7676         struct statfs st_fs;
> >  7677         char *dname, *dir;
> >  7678         int err = 0;
> >  7679
> >  7680         if (path == NULL)
> >  7681                 return -EINVAL;
> >  7682
> >  7683         dname = strdup(path);
> >  7684         if (dname == NULL)
> >  7685                 return -ENOMEM;
> >  7686
> >  7687         dir = dirname(dname);
> >  7688         if (statfs(dir, &st_fs)) {
> >  7689                 cp = libbpf_strerror_r(errno, errmsg,
> > sizeof(errmsg));
> >  7690                 pr_warn("failed to statfs %s: %s\n", dir, cp);
> >  7691                 err = -errno;
> >  7692         }
> >  7693         free(dname);
> >  7694
> >  7695         if (!err && st_fs.f_type != BPF_FS_MAGIC) {
> >  7696                 pr_warn("specified path %s is not on BPF FS\n",
> > path);
> >  7697                 err = -EINVAL;
> >  7698         }
> >  7699
> >  7700         return err;
> >  7701 }
>
> Thanks.
>
>
> 在 2022/4/22 0:55, Andrii Nakryiko 写道:
> > On Thu, Apr 21, 2022 at 6:01 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
> >> The make_parent_dir is called without null-pointer checking for path,
> >> such as bpf_link__pin. To ensure there is no null-pointer dereference
> >> in make_parent_dir, so make_parent_dir requires additional null-pointer
> >> checking for path.
> >>
> >> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
> >> ---
> >>   tools/lib/bpf/libbpf.c | 3 +++
> >>   1 file changed, 3 insertions(+)
> >>
> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> >> index b53e51884f9e..5786e6184bf5 100644
> >> --- a/tools/lib/bpf/libbpf.c
> >> +++ b/tools/lib/bpf/libbpf.c
> >> @@ -7634,6 +7634,9 @@ static int make_parent_dir(const char *path)
> >>          char *dname, *dir;
> >>          int err = 0;
> >>
> >> +       if (path == NULL)
> >> +               return -EINVAL;
> >> +
> > API contract is that path shouldn't be NULL. Just like we don't check
> > link, obj, prog for NULL in every single API, I don't think we need to
> > do it here, unless I'm missing something?
> >
> >>          dname = strdup(path);
> >>          if (dname == NULL)
> >>                  return -ENOMEM;
> >> --
> >> 2.25.1
> >>
> > .