From 71876dffab295b6e25d4209f0424da8fc5020e12 Mon Sep 17 00:00:00 2001 From: "Masami Hiramatsu (Google)" Date: Thu, 26 Mar 2026 21:12:00 +0900 Subject: [PATCH 1/2] lib/vsprintf: Fix to check field_width and precision 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 Closes: https://lore.kernel.org/all/20260318151250.40fef0ab@pumpkin/ Signed-off-by: Masami Hiramatsu (Google) Reviewed-by: Petr Mladek Link: https://patch.msgid.link/177452712047.197965.16376597502504928495.stgit@devnote2 Signed-off-by: Petr Mladek --- lib/vsprintf.c | 36 ++++++++++++++---------------------- 1 file changed, 14 insertions(+), 22 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 9f359b31c8d1..3c76cc5c7f9c 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. From e56185668dc12983dd0e75e38ed6dea98b01d2d2 Mon Sep 17 00:00:00 2001 From: "Masami Hiramatsu (Google)" Date: Thu, 26 Mar 2026 21:12:10 +0900 Subject: [PATCH 2/2] lib/vsprintf: Limit the returning size to INT_MAX The return value of vsnprintf() and bstr_printf() can overflow INT_MAX and return a minus value. In the @size is checked input overflow, but it does not check the output, which is expected required size. This should never happen but it should be checked and limited. Signed-off-by: Masami Hiramatsu (Google) Reviewed-by: Petr Mladek Link: https://patch.msgid.link/177452713020.197965.3164174544083829000.stgit@devnote2 Signed-off-by: Petr Mladek --- lib/vsprintf.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 3c76cc5c7f9c..6b1213d070b4 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -2856,6 +2856,7 @@ static unsigned long long convert_num_spec(unsigned int val, int size, struct pr int vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args) { char *str, *end; + size_t ret_size; struct printf_spec spec = {0}; struct fmt fmt = { .str = fmt_str, @@ -2975,8 +2976,12 @@ int vsnprintf(char *buf, size_t size, const char *fmt_str, va_list args) } /* the trailing null byte doesn't count towards the total */ - return str-buf; + ret_size = str - buf; + /* Make sure the return value is within the positive integer range */ + if (WARN_ON_ONCE(ret_size > INT_MAX)) + ret_size = INT_MAX; + return ret_size; } EXPORT_SYMBOL(vsnprintf); @@ -3280,6 +3285,7 @@ int bstr_printf(char *buf, size_t size, const char *fmt_str, const u32 *bin_buf) struct printf_spec spec = {0}; char *str, *end; const char *args = (const char *)bin_buf; + size_t ret_size; if (WARN_ON_ONCE(size > INT_MAX)) return 0; @@ -3428,7 +3434,12 @@ int bstr_printf(char *buf, size_t size, const char *fmt_str, const u32 *bin_buf) #undef get_arg /* the trailing null byte doesn't count towards the total */ - return str - buf; + ret_size = str - buf; + + /* Make sure the return value is within the positive integer range */ + if (WARN_ON_ONCE(ret_size > INT_MAX)) + ret_size = INT_MAX; + return ret_size; } EXPORT_SYMBOL_GPL(bstr_printf);