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Subject[PATCH v4 4/9] vsprintf: Consolidate handling of unknown pointer specifiers
Date
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 <pmladek@suse.com>
---
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
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