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bpf: Reject %p% format string in bprintf-like helpers

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[ 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: 48cac3f4a9 ("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.1751395489.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Paul Chaignon
2025-07-01 21:47:30 +02:00
committed by Greg Kroah-Hartman
parent 12e023df10
commit e7be679124
1 changed files with 8 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
kernel/bpf/helpers.c
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@@ -885,6 +885,13 @@ 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];
@@ -892,11 +899,9 @@ 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++;