Messages in this thread Patch in this message |  | | From | "Masami Hiramatsu (Google)" <> | | Subject | [PATCH v6 1/2] lib/vsprintf: Fix to check field_width and precision | | Date | Thu, 26 Mar 2026 21:12:00 +0900 |
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From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Check the field_width and presition correctly. Previously it depends on the bitfield conversion from int to check out-of-range error. However, commit 938df695e98d ("vsprintf: associate the format state with the format pointer") changed those fields to int. We need to check the out-of-range correctly without bitfield conversion.
Fixes: 938df695e98d ("vsprintf: associate the format state with the format pointer") Reported-by: David Laight <david.laight.linux@gmail.com> Closes: https://lore.kernel.org/all/20260318151250.40fef0ab@pumpkin/ Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> --- Changes in v6: - Make the function header of set_field_width() and set_precision(), and WARN_ONCE() to be one line. Changes in v5: - Drop negative precision support. - The field and precision passed as string literals are also checked. Changes in v4: - Do clamp() first. - Accept negative precision (this means no precision) . - Change the warning message for width. Changes in v3: - Check and update width and precision before assigning to spec. Changes in v2: - Fix to use logical split. --- lib/vsprintf.c | 36 ++++++++++++++---------------------- 1 file changed, 14 insertions(+), 22 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 800b8ac49f53..10a1b21c8920 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -2640,6 +2640,18 @@ static unsigned char spec_flag(unsigned char c) return (c < sizeof(spec_flag_array)) ? spec_flag_array[c] : 0; } +static void set_field_width(struct printf_spec *spec, int width) +{ + spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX); + WARN_ONCE(spec->field_width != width, "field width %d out of range", width); +} + +static void set_precision(struct printf_spec *spec, int prec) +{ + spec->precision = clamp(prec, 0, PRECISION_MAX); + WARN_ONCE(spec->precision < prec, "precision %d too large", prec); +} + /* * Helper function to decode printf style format. * Each call decode a token from the format and return the @@ -2710,7 +2722,7 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec) spec->field_width = -1; if (isdigit(*fmt.str)) - spec->field_width = skip_atoi(&fmt.str); + set_field_width(spec, skip_atoi(&fmt.str)); else if (unlikely(*fmt.str == '*')) { /* it's the next argument */ fmt.state = FORMAT_STATE_WIDTH; @@ -2724,9 +2736,7 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec) if (unlikely(*fmt.str == '.')) { fmt.str++; if (isdigit(*fmt.str)) { - spec->precision = skip_atoi(&fmt.str); - if (spec->precision < 0) - spec->precision = 0; + set_precision(spec, skip_atoi(&fmt.str)); } else if (*fmt.str == '*') { /* it's the next argument */ fmt.state = FORMAT_STATE_PRECISION; @@ -2799,24 +2809,6 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec) return fmt; } -static void -set_field_width(struct printf_spec *spec, int width) -{ - spec->field_width = width; - if (WARN_ONCE(spec->field_width != width, "field width %d too large", width)) { - spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX); - } -} - -static void -set_precision(struct printf_spec *spec, int prec) -{ - spec->precision = prec; - if (WARN_ONCE(spec->precision != prec, "precision %d too large", prec)) { - spec->precision = clamp(prec, 0, PRECISION_MAX); - } -} - /* * Turn a 1/2/4-byte value into a 64-bit one for printing: truncate * as necessary and deal with signedness.
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