6.1-stable review patch. If anyone has any objections, please let me know.
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From: Paul Chaignon paul.chaignon@gmail.com
[ Upstream commit f8242745871f81a3ac37f9f51853d12854fd0b58 ]
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@syzkaller.appspotmail.com Fixes: 48cac3f4a96d ("bpf: Implement formatted output helpers with bstr_printf") Acked-by: Yonghong Song yonghong.song@linux.dev Signed-off-by: Paul Chaignon paul.chaignon@gmail.com Link: https://lore.kernel.org/r/a0e06cc479faec9e802ae51ba5d66420523251ee.175139548... Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 94e85d311641b..be9dc396537f1 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -876,6 +876,13 @@ 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]; @@ -883,11 +890,9 @@ 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++;