[PATCHv3 bpf-next 09/12] bpf: Clear buf on error in __bpf_get_task_stack

[Jiri Olsa <jolsa@kernel.org>]

Both bpf_get_task_stack and bpf_get_task_stack_sleepable helpers that
use __bpf_get_task_stack have buf defined as ARG_PTR_TO_UNINIT_MEM
argument and we should initialize the buf on every return path.

Adding missing buf memset for __bpf_get_task_stack fail paths. This
provides deterministic buffer contents, which is useful when the buffer
is used directly as a map key.

Fixes: 06ab134ce8ec ("bpf: Refcount task stack in bpf_get_task_stack")
Fixes: b992f01e6615 ("bpf: Guard against accessing NULL pt_regs in bpf_get_task_stack()")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 kernel/bpf/stackmap.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 976c4e4c1af6..7f728d319a65 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -884,14 +884,17 @@ static long __bpf_get_task_stack(struct task_struct *task, void *buf, u32 size,
 	struct pt_regs *regs;
 	long res = -EINVAL;
 
-	if (!try_get_task_stack(task))
+	if (!try_get_task_stack(task)) {
+		memset(buf, 0, size);
 		return -EFAULT;
+	}
 
 	regs = task_pt_regs(task);
 	if (regs)
 		res = __bpf_get_stack(regs, task, buf, size, flags, may_fault);
+	else
+		memset(buf, 0, size);
 	put_task_stack(task);
-
 	return res;
 }
 
-- 
2.54.0