Re: [PATCH] bpf: dereference of null in __cgroup_bpf_query() function

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On 4/6/24 8:14 AM, Mikhail Lobanov wrote:
In the __cgroup_bpf_query() function, it is possible to dereference
the null pointer in the line id = prog->aux->id; since there is no
check for a non-zero value of the variable prog.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: af6eea57437a ("bpf: Implement bpf_link-based cgroup BPF program attachment")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mikhail Lobanov <m.lobanov@xxxxxxxxxxxx>
---
  kernel/bpf/cgroup.c | 2 ++
  1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 491d20038cbe..7f2db96f0c6a 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1092,6 +1092,8 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
  			i = 0;
  			hlist_for_each_entry(pl, progs, node) {
  				prog = prog_list_prog(pl);
+               	       	if (!prog_list_prog(pl))

prog cannot be null. It is under cgroup_lock().

+				continue;
  				id = prog->aux->id;
  				if (copy_to_user(prog_ids + i, &id, sizeof(id)))
  					return -EFAULT;





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