Hi,
Static analysis with Coverity on linux-next has detected a potential
issue with the following commit:
commit b89fbfbb854c9afc3047e8273cc3a694650b802e
Author: Andrii Nakryiko [off-list ref]
Date: Sun Aug 15 00:05:57 2021 -0700
bpf: Implement minimal BPF perf link
The analysis is as follows:
2936 static int bpf_perf_link_attach(const union bpf_attr *attr, struct
bpf_prog *prog)
2937 {
1. var_decl: Declaring variable link_primer without initializer.
2938 struct bpf_link_primer link_primer;
2939 struct bpf_perf_link *link;
2940 struct perf_event *event;
2941 struct file *perf_file;
2942 int err;
2943
2. Condition attr->link_create.flags, taking false branch.
2944 if (attr->link_create.flags)
2945 return -EINVAL;
2946
2947 perf_file = perf_event_get(attr->link_create.target_fd);
3. Condition IS_ERR(perf_file), taking false branch.
2948 if (IS_ERR(perf_file))
2949 return PTR_ERR(perf_file);
2950
2951 link = kzalloc(sizeof(*link), GFP_USER);
4. Condition !link, taking false branch.
2952 if (!link) {
2953 err = -ENOMEM;
2954 goto out_put_file;
2955 }
2956 bpf_link_init(&link->link, BPF_LINK_TYPE_PERF_EVENT,
&bpf_perf_link_lops, prog);
2957 link->perf_file = perf_file;
2958
2959 err = bpf_link_prime(&link->link, &link_primer);
5. Condition err, taking false branch.
2960 if (err) {
2961 kfree(link);
2962 goto out_put_file;
2963 }
2964
2965 event = perf_file->private_data;
2966 err = perf_event_set_bpf_prog(event, prog,
attr->link_create.perf_event.bpf_cookie);
6. Condition err, taking true branch.
2967 if (err) {
7. uninit_use_in_call: Using uninitialized value link_primer.fd when
calling bpf_link_cleanup.
8. uninit_use_in_call: Using uninitialized value link_primer.file
when calling bpf_link_cleanup.
9. uninit_use_in_call: Using uninitialized value link_primer.id when
calling bpf_link_cleanup.
Uninitialized pointer read (UNINIT)
10. uninit_use_in_call: Using uninitialized value link_primer.link
when calling bpf_link_cleanup.
2968 bpf_link_cleanup(&link_primer);
2969 goto out_put_file;
2970 }
2971 /* perf_event_set_bpf_prog() doesn't take its own refcnt on
prog */
2972 bpf_prog_inc(prog);
I'm not 100% sure if these are false-positives, but I thought I should
report the issues as potentially there is a pointer access on an
uninitialized pointer on line 2968.
Colin
On Tue, Aug 17, 2021 at 10:36 AM Colin Ian King
[off-list ref] wrote:
Hi,
Static analysis with Coverity on linux-next has detected a potential
issue with the following commit:
commit b89fbfbb854c9afc3047e8273cc3a694650b802e
Author: Andrii Nakryiko [off-list ref]
Date: Sun Aug 15 00:05:57 2021 -0700
bpf: Implement minimal BPF perf link
The analysis is as follows:
2936 static int bpf_perf_link_attach(const union bpf_attr *attr, struct
bpf_prog *prog)
2937 {
1. var_decl: Declaring variable link_primer without initializer.
2938 struct bpf_link_primer link_primer;
2939 struct bpf_perf_link *link;
2940 struct perf_event *event;
2941 struct file *perf_file;
2942 int err;
2943
2. Condition attr->link_create.flags, taking false branch.
2944 if (attr->link_create.flags)
2945 return -EINVAL;
2946
2947 perf_file = perf_event_get(attr->link_create.target_fd);
3. Condition IS_ERR(perf_file), taking false branch.
2948 if (IS_ERR(perf_file))
2949 return PTR_ERR(perf_file);
2950
2951 link = kzalloc(sizeof(*link), GFP_USER);
4. Condition !link, taking false branch.
2952 if (!link) {
2953 err = -ENOMEM;
2954 goto out_put_file;
2955 }
2956 bpf_link_init(&link->link, BPF_LINK_TYPE_PERF_EVENT,
&bpf_perf_link_lops, prog);
2957 link->perf_file = perf_file;
2958
2959 err = bpf_link_prime(&link->link, &link_primer);
5. Condition err, taking false branch.
2960 if (err) {
2961 kfree(link);
2962 goto out_put_file;
2963 }
2964
2965 event = perf_file->private_data;
2966 err = perf_event_set_bpf_prog(event, prog,
attr->link_create.perf_event.bpf_cookie);
6. Condition err, taking true branch.
2967 if (err) {
7. uninit_use_in_call: Using uninitialized value link_primer.fd when
calling bpf_link_cleanup.
8. uninit_use_in_call: Using uninitialized value link_primer.file
when calling bpf_link_cleanup.
9. uninit_use_in_call: Using uninitialized value link_primer.id when
calling bpf_link_cleanup.
Uninitialized pointer read (UNINIT)
10. uninit_use_in_call: Using uninitialized value link_primer.link
when calling bpf_link_cleanup.
2968 bpf_link_cleanup(&link_primer);
2969 goto out_put_file;
2970 }
2971 /* perf_event_set_bpf_prog() doesn't take its own refcnt on
prog */
2972 bpf_prog_inc(prog);
I'm not 100% sure if these are false-positives, but I thought I should
report the issues as potentially there is a pointer access on an
uninitialized pointer on line 2968.
Look at bpf_link_prime() implementation. If it succeeds, link_primer
is fully initialized. We use this pattern in many places, this is the
first time someone reports any potential issues with it. It's a bit
strange that Coverity doesn't recognize such a typical output
parameter initialization pattern, tbh. Maybe the global nature of
bpf_link_prime() throws it off (it assumes it can be "overridden"
during linking?) But I double-checked everything twice, all seems to
be good. Zero-initializing link_primer would be a total waste.
Colin
On 17/08/2021 19:57, Andrii Nakryiko wrote:
On Tue, Aug 17, 2021 at 10:36 AM Colin Ian King
[off-list ref] wrote:
quoted
Hi,
Static analysis with Coverity on linux-next has detected a potential
issue with the following commit:
commit b89fbfbb854c9afc3047e8273cc3a694650b802e
Author: Andrii Nakryiko [off-list ref]
Date: Sun Aug 15 00:05:57 2021 -0700
bpf: Implement minimal BPF perf link
The analysis is as follows:
2936 static int bpf_perf_link_attach(const union bpf_attr *attr, struct
bpf_prog *prog)
2937 {
1. var_decl: Declaring variable link_primer without initializer.
2938 struct bpf_link_primer link_primer;
2939 struct bpf_perf_link *link;
2940 struct perf_event *event;
2941 struct file *perf_file;
2942 int err;
2943
2. Condition attr->link_create.flags, taking false branch.
2944 if (attr->link_create.flags)
2945 return -EINVAL;
2946
2947 perf_file = perf_event_get(attr->link_create.target_fd);
3. Condition IS_ERR(perf_file), taking false branch.
2948 if (IS_ERR(perf_file))
2949 return PTR_ERR(perf_file);
2950
2951 link = kzalloc(sizeof(*link), GFP_USER);
4. Condition !link, taking false branch.
2952 if (!link) {
2953 err = -ENOMEM;
2954 goto out_put_file;
2955 }
2956 bpf_link_init(&link->link, BPF_LINK_TYPE_PERF_EVENT,
&bpf_perf_link_lops, prog);
2957 link->perf_file = perf_file;
2958
2959 err = bpf_link_prime(&link->link, &link_primer);
5. Condition err, taking false branch.
2960 if (err) {
2961 kfree(link);
2962 goto out_put_file;
2963 }
2964
2965 event = perf_file->private_data;
2966 err = perf_event_set_bpf_prog(event, prog,
attr->link_create.perf_event.bpf_cookie);
6. Condition err, taking true branch.
2967 if (err) {
7. uninit_use_in_call: Using uninitialized value link_primer.fd when
calling bpf_link_cleanup.
8. uninit_use_in_call: Using uninitialized value link_primer.file
when calling bpf_link_cleanup.
9. uninit_use_in_call: Using uninitialized value link_primer.id when
calling bpf_link_cleanup.
Uninitialized pointer read (UNINIT)
10. uninit_use_in_call: Using uninitialized value link_primer.link
when calling bpf_link_cleanup.
2968 bpf_link_cleanup(&link_primer);
2969 goto out_put_file;
2970 }
2971 /* perf_event_set_bpf_prog() doesn't take its own refcnt on
prog */
2972 bpf_prog_inc(prog);
I'm not 100% sure if these are false-positives, but I thought I should
report the issues as potentially there is a pointer access on an
uninitialized pointer on line 2968.
Look at bpf_link_prime() implementation. If it succeeds, link_primer
is fully initialized. We use this pattern in many places, this is the
first time someone reports any potential issues with it. It's a bit
strange that Coverity doesn't recognize such a typical output
parameter initialization pattern, tbh. Maybe the global nature of
bpf_link_prime() throws it off (it assumes it can be "overridden"
during linking?) But I double-checked everything twice, all seems to
be good. Zero-initializing link_primer would be a total waste.
Yes, in pedantic mode it can throw false positives, it's not perfect.
Thanks for double checking, and apologies for wasting your valuable time.
Colin
quoted
Colin