From: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Date: Sat, 14 Aug 2021 10:57:16 +0900
Subject: bpf: Support "%c" in bpf_bprintf_prepare().
Patch-mainline: v5.15-rc1
Git-commit: 3478cfcfcddff0f3aad82891be2992e51c4f7936
References: jsc#PED-1377

/proc/net/unix uses "%c" to print a single-byte character to escape '\0' in
the name of the abstract UNIX domain socket.  The following selftest uses
it, so this patch adds support for "%c".  Note that it does not support
wide character ("%lc" and "%llc") for simplicity.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210814015718.42704-3-kuniyu@amazon.co.jp
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/helpers.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -918,6 +918,20 @@ fmt_str:
 			num_spec++;
 
 			continue;
+		} else if (fmt[i] == 'c') {
+			if (!tmp_buf)
+				goto nocopy_fmt;
+
+			if (tmp_buf_end == tmp_buf) {
+				err = -ENOSPC;
+				goto out;
+			}
+
+			*tmp_buf = raw_args[num_spec];
+			tmp_buf++;
+			num_spec++;
+
+			continue;
 		}
 
 		sizeof_cur_arg = sizeof(int);