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Subject[PATCH v5 05/11] 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)".

Using WARN() looks like an overkill for this type of error. pr_warn()
is not good either. It would by handled via printk_sage buffer and
it might be hard to match it with the problematic string.

A reasonable compromise seems to be writing the unknown format specifier
into the original string with a question mark, for example (%pC?).
It should be self-explaining enough. Note that it is in brackets
to follow the (null) style.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
lib/vsprintf.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 5c26a4e71cdf..587175a528b7 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1488,7 +1488,8 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
}

static noinline_for_stack
-char *netdev_bits(char *buf, char *end, const void *addr, const char *fmt)
+char *netdev_bits(char *buf, char *end, const void *addr,
+ struct printf_spec spec, const char *fmt)
{
unsigned long long num;
int size;
@@ -1499,9 +1500,7 @@ 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;
+ return valid_string(buf, end, "(%pN?)", spec);
}

return special_hex_number(buf, end, num, size);
@@ -1532,7 +1531,10 @@ 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))
+ return valid_string(buf, end, "(%pC?)", spec);
+
+ if (!clk)
return string(buf, end, NULL, spec);

switch (fmt[1]) {
@@ -1544,7 +1546,7 @@ 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));
+ return valid_string(buf, end, "(%pC?)", spec);
#endif
}
}
@@ -1577,7 +1579,8 @@ char *format_flags(char *buf, char *end, unsigned long flags,
}

static noinline_for_stack
-char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt)
+char *flags_string(char *buf, char *end, void *flags_ptr,
+ struct printf_spec spec, const char *fmt)
{
unsigned long flags;
const struct trace_print_flags *names;
@@ -1598,8 +1601,7 @@ 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]);
- return buf;
+ return valid_string(buf, end, "(%pG?)", spec);
}

return format_flags(buf, end, flags, names);
@@ -1655,7 +1657,7 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
str_spec.field_width = -1;

if (!IS_ENABLED(CONFIG_OF))
- return valid_string(buf, end, "(!OF)", spec);
+ return valid_string(buf, end, "(%OF?)", spec);

if ((unsigned long)dn < PAGE_SIZE)
return valid_string(buf, end, "(null)", spec);
@@ -1926,7 +1928,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
case 'K':
return restricted_pointer(buf, end, ptr, spec);
case 'N':
- return netdev_bits(buf, end, ptr, fmt);
+ return netdev_bits(buf, end, ptr, spec, fmt);
case 'a':
return address_val(buf, end, ptr, fmt);
case 'd':
@@ -1943,7 +1945,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
#endif

case 'G':
- return flags_string(buf, end, ptr, fmt);
+ return flags_string(buf, end, ptr, spec, fmt);
case 'O':
switch (fmt[1]) {
case 'F':
--
2.13.6
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