[PATCH bpf] bpf: fix a task_iter bug caused by a merge conflict resolution

[PATCH bpf] bpf: fix a task_iter bug caused by a merge conflict resolution

[Yonghong Song]

Latest bpf tree has a bug for bpf_iter selftest.
  $ ./test_progs -n 4/25
  test_bpf_sk_storage_get:PASS:bpf_iter_bpf_sk_storage_helpers__open_and_load 0 nsec
  test_bpf_sk_storage_get:PASS:socket 0 nsec
  ...
  do_dummy_read:PASS:read 0 nsec
  test_bpf_sk_storage_get:FAIL:bpf_map_lookup_elem map value wasn't set correctly
                          (expected 1792, got -1, err=0)
  #4/25 bpf_sk_storage_get:FAIL
  #4 bpf_iter:FAIL
  Summary: 0/0 PASSED, 0 SKIPPED, 2 FAILED

When doing merge conflict resolution, Commit 4bfc4714849d missed to
save curr_task to seq_file private data. The task pointer in seq_file
private data is passed to bpf program. This caused
NULL-pointer task passed to bpf program which will immediately return
upon checking whether task pointer is NULL.

This patch added back the assignment of curr_task to seq_file private data
and fixed the issue.

Fixes: 4bfc4714849d ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/bpf/task_iter.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 3efe38191d1c..175b7b42bfc4 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -159,6 +159,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
                 }
 
                 /* set info->task and info->tid */
+		info->task = curr_task;
 		if (curr_tid == info->tid) {
 			curr_fd = info->fd;
 		} else {
-- 
2.24.1

RE: [PATCH bpf] bpf: fix a task_iter bug caused by a merge conflict resolution

[John Fastabend]

Yonghong Song wrote:
> Latest bpf tree has a bug for bpf_iter selftest.
>   $ ./test_progs -n 4/25
>   test_bpf_sk_storage_get:PASS:bpf_iter_bpf_sk_storage_helpers__open_and_load 0 nsec
>   test_bpf_sk_storage_get:PASS:socket 0 nsec
>   ...
>   do_dummy_read:PASS:read 0 nsec
>   test_bpf_sk_storage_get:FAIL:bpf_map_lookup_elem map value wasn't set correctly
>                           (expected 1792, got -1, err=0)
>   #4/25 bpf_sk_storage_get:FAIL
>   #4 bpf_iter:FAIL
>   Summary: 0/0 PASSED, 0 SKIPPED, 2 FAILED
> 
> When doing merge conflict resolution, Commit 4bfc4714849d missed to
> save curr_task to seq_file private data. The task pointer in seq_file
> private data is passed to bpf program. This caused
> NULL-pointer task passed to bpf program which will immediately return
> upon checking whether task pointer is NULL.
> 
> This patch added back the assignment of curr_task to seq_file private data
> and fixed the issue.
> 
> Fixes: 4bfc4714849d ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf")
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  kernel/bpf/task_iter.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index 3efe38191d1c..175b7b42bfc4 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -159,6 +159,7 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
>                  }
>  
>                  /* set info->task and info->tid */
> +		info->task = curr_task;
>  		if (curr_tid == info->tid) {
>  			curr_fd = info->fd;
>  		} else {
> -- 
> 2.24.1
> 

Acked-by: John Fastabend <john.fastabend@gmail.com>

Re: [PATCH bpf] bpf: fix a task_iter bug caused by a merge conflict resolution

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (refs/heads/master):

On Wed, 30 Dec 2020 21:24:18 -0800 you wrote:
> Latest bpf tree has a bug for bpf_iter selftest.
>   $ ./test_progs -n 4/25
>   test_bpf_sk_storage_get:PASS:bpf_iter_bpf_sk_storage_helpers__open_and_load 0 nsec
>   test_bpf_sk_storage_get:PASS:socket 0 nsec
>   ...
>   do_dummy_read:PASS:read 0 nsec
>   test_bpf_sk_storage_get:FAIL:bpf_map_lookup_elem map value wasn't set correctly
>                           (expected 1792, got -1, err=0)
>   #4/25 bpf_sk_storage_get:FAIL
>   #4 bpf_iter:FAIL
>   Summary: 0/0 PASSED, 0 SKIPPED, 2 FAILED
> 
> [...]

Here is the summary with links:
  - [bpf] bpf: fix a task_iter bug caused by a merge conflict resolution
    https://git.kernel.org/bpf/bpf/c/04901aab40ea

You are awesome, thank you!
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