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bpf: allow UTF-8 literals in bpf_bprintf_prepare()

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bpf_bprintf_prepare() only needs ASCII parsing for conversion
specifiers. Plain text can safely carry bytes >= 0x80, so allow
UTF-8 literals outside '%' sequences while keeping ASCII control
bytes rejected and format specifiers ASCII-only.

This keeps existing parsing rules for format directives unchanged,
while allowing helpers such as bpf_trace_printk() to emit UTF-8
literal text.

Update test_snprintf_negative() in the same commit so selftests keep
matching the new plain-text vs format-specifier split during bisection.

Fixes: 48cac3f4a9 ("bpf: Implement formatted output helpers with bstr_printf")
Signed-off-by: Yihan Ding <dingyihan@uniontech.com>
Acked-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/20260416120142.1420646-2-dingyihan@uniontech.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yihan Ding
2026-04-16 20:01:41 +08:00
committed by Alexei Starovoitov
parent 766bf026d0
commit b960430ea8
2 changed files with 18 additions and 2 deletions
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17
kernel/bpf/helpers.c
View File

@@ -845,7 +845,13 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
data->buf = buffers->buf;
for (i = 0; i < fmt_size; i++) {
if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i])) {
unsigned char c = fmt[i];
/*
* Permit bytes >= 0x80 in plain text so UTF-8 literals can pass
* through unchanged, while still rejecting ASCII control bytes.
*/
if (isascii(c) && !isprint(c) && !isspace(c)) {
err = -EINVAL;
goto out;
}
@@ -867,6 +873,15 @@ int bpf_bprintf_prepare(const char *fmt, u32 fmt_size, const u64 *raw_args,
* always access fmt[i + 1], in the worst case it will be a 0
*/
i++;
c = fmt[i];
/*
* The format parser below only understands ASCII conversion
* specifiers and modifiers, so reject non-ASCII after '%'.
*/
if (!isascii(c)) {
err = -EINVAL;
goto out;
}
/* skip optional "[0 +-][num]" width formatting field */
while (fmt[i] == '0' || fmt[i] == '+' || fmt[i] == '-' ||

3
tools/testing/selftests/bpf/prog_tests/snprintf.c
View File

@@ -114,7 +114,8 @@ static void test_snprintf_negative(void)
ASSERT_ERR(load_single_snprintf("%--------"), "invalid specifier 5");
ASSERT_ERR(load_single_snprintf("%lc"), "invalid specifier 6");
ASSERT_ERR(load_single_snprintf("%llc"), "invalid specifier 7");
ASSERT_ERR(load_single_snprintf("\x80"), "non ascii character");
ASSERT_OK(load_single_snprintf("\x80"), "non ascii plain text");
ASSERT_ERR(load_single_snprintf("%\x80"), "non ascii in specifier");
ASSERT_ERR(load_single_snprintf("\x1"), "non printable character");
ASSERT_ERR(load_single_snprintf("%p%"), "invalid specifier 8");
ASSERT_ERR(load_single_snprintf("%s%"), "invalid specifier 9");