There are few printk formats that make sense only with two or more specifiers. Also some specifiers make sense only when a kernel feature is enabled.
The handling of unknown specifiers is strange, inconsistent, and even leaking the address. For example, netdev_bits() prints the non-hashed pointer value or clock() prints "(null)". The best solution seems to be in flags_string(). It does not print any misleading value. Instead it calls WARN_ONCE() describing the unknown specifier. Therefore it clearly shows the problem and helps to find it. Note that WARN_ONCE() used to cause recursive printk(). But it is safe now because vscnprintf() is called in printk_safe context from vprintk_emit(). Signed-off-by: Petr Mladek <[email protected]> --- lib/vsprintf.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/lib/vsprintf.c b/lib/vsprintf.c index dd71738d7a09..5a0d01846a11 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1484,9 +1484,9 @@ char *netdev_bits(char *buf, char *end, const void *addr, const char *fmt) size = sizeof(netdev_features_t); break; default: - num = (unsigned long)addr; - size = sizeof(unsigned long); - break; + WARN_ONCE(1, "Unsupported pointer format specifier: %%pN%c\n", + fmt[1]); + return buf; } return special_hex_number(buf, end, num, size); @@ -1517,7 +1517,12 @@ static noinline_for_stack char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec, const char *fmt) { - if (!IS_ENABLED(CONFIG_HAVE_CLK) || !clk) + if (!IS_ENABLED(CONFIG_HAVE_CLK)) { + WARN_ONCE(1, "Unsupported pointer format specifier: %%pC\n"); + return buf; + } + + if (!clk) return string(buf, end, NULL, spec); switch (fmt[1]) { @@ -1529,7 +1534,8 @@ char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec, #ifdef CONFIG_COMMON_CLK return string(buf, end, __clk_get_name(clk), spec); #else - return special_hex_number(buf, end, (unsigned long)clk, sizeof(unsigned long)); + WARN_ONCE(1, "Unsupported pointer format specifier: %%pC\n"); + return buf; #endif } } @@ -1593,7 +1599,8 @@ char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt) names = gfpflag_names; break; default: - WARN_ONCE(1, "Unsupported flags modifier: %c\n", fmt[1]); + WARN_ONCE(1, "Unsupported pointer format specifier: %%pG%c\n", + fmt[1]); return buf; } -- 2.13.6
