static const char fmt[] = "%p%";
bpf_trace_printk(fmt, sizeof(fmt));
The above BPF program isn't rejected and causes a kernel warning at
runtime:
Please remove unsupported %\x00 in format string
WARNING: CPU: 1 PID: 7244 at lib/vsprintf.c:2680 format_decode+0x49c/0x5d0
This happens because bpf_bprintf_prepare skips over the second %,
detected as punctuation, while processing %p. This patch fixes it by
not skipping over punctuation. %\x00 is then processed in the next
iteration and rejected.
Reported-by: syzbot+e2c932aec5c8a6e1d31c@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf")
Signed-off-by: Paul Chaignon <paul.chaignon@xxxxxxxxx>
---
kernel/bpf/helpers.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b71e428ad936..ad6df48b540c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -884,6 +884,13 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
if (fmt[i] == 'p') {
sizeof_cur_arg = sizeof(long);
+ if (fmt[i + 1] == 0 || isspace(fmt[i + 1]) ||
+ ispunct(fmt[i + 1])) {
+ if (tmp_buf)
+ cur_arg = raw_args[num_spec];
+ goto nocopy_fmt;
+ }
+
if ((fmt[i + 1] == 'k' || fmt[i + 1] == 'u') &&
fmt[i + 2] == 's') {
fmt_ptype = fmt[i + 1];
@@ -891,11 +898,9 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
goto fmt_str;
}
- if (fmt[i + 1] == 0 || isspace(fmt[i + 1]) ||
- ispunct(fmt[i + 1]) || fmt[i + 1] == 'K' ||
+ if (fmt[i + 1] == 'K' ||
fmt[i + 1] == 'x' || fmt[i + 1] == 's' ||
fmt[i + 1] == 'S') {
- /* just kernel pointers */
if (tmp_buf)
cur_arg = raw_args[num_spec];
i++;
--
2.43.0
