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authorTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>2018-12-04 19:00:01 +0900
committerPetr Mladek <pmladek@suse.com>2018-12-10 10:45:59 +0100
commite80c1a9d5f514ce5134c6c4263a11607341466c9 (patch)
tree9809c5253e849d33edd885322a2a925ae25e1937 /kernel/printk
parent9adcfaffc34d53e498637237fb3701560359d50b (diff)
downloadlinux-e80c1a9d5f514ce5134c6c4263a11607341466c9.tar.bz2
printk: fix printk_time race.
Since printk_time can be toggled via /sys/module/printk/parameters/time , it is not safe to assume that output length does not change across multiple msg_print_text() calls. If we hit this race, we can observe failures such as SYSLOG_ACTION_READ_ALL writes more bytes than userspace has supplied, SYSLOG_ACTION_SIZE_UNREAD returns -EFAULT when succeeded, SYSLOG_ACTION_READ reads garbage memory or even triggers an kernel oops at _copy_to_user() due to integer overflow. To close this race, get a snapshot value of printk_time and pass it to SYSLOG_ACTION_READ, SYSLOG_ACTION_READ_ALL, SYSLOG_ACTION_SIZE_UNREAD and kmsg_dump_get_buffer(). Link: http://lkml.kernel.org/r/555af37c-b9e0-f940-cb73-a78eba2d4944@i-love.sakura.ne.jp To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Petr Mladek <pmladek@suse.com>
Diffstat (limited to 'kernel/printk')
-rw-r--r--kernel/printk/printk.c70
1 files changed, 39 insertions, 31 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a1d88212a5d2..c7d217764db3 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -404,6 +404,7 @@ DECLARE_WAIT_QUEUE_HEAD(log_wait);
static u64 syslog_seq;
static u32 syslog_idx;
static size_t syslog_partial;
+static bool syslog_time;
/* index and sequence number of the first record stored in the buffer */
static u64 log_first_seq;
@@ -1229,12 +1230,7 @@ module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
static size_t print_time(u64 ts, char *buf)
{
- unsigned long rem_nsec;
-
- if (!printk_time)
- return 0;
-
- rem_nsec = do_div(ts, 1000000000);
+ unsigned long rem_nsec = do_div(ts, 1000000000);
if (!buf)
return snprintf(NULL, 0, "[%5lu.000000] ", (unsigned long)ts);
@@ -1243,7 +1239,8 @@ static size_t print_time(u64 ts, char *buf)
(unsigned long)ts, rem_nsec / 1000);
}
-static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
+static size_t print_prefix(const struct printk_log *msg, bool syslog,
+ bool time, char *buf)
{
size_t len = 0;
unsigned int prefix = (msg->facility << 3) | msg->level;
@@ -1262,11 +1259,13 @@ static size_t print_prefix(const struct printk_log *msg, bool syslog, char *buf)
}
}
- len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
+ if (time)
+ len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
return len;
}
-static size_t msg_print_text(const struct printk_log *msg, bool syslog, char *buf, size_t size)
+static size_t msg_print_text(const struct printk_log *msg, bool syslog,
+ bool time, char *buf, size_t size)
{
const char *text = log_text(msg);
size_t text_size = msg->text_len;
@@ -1285,17 +1284,17 @@ static size_t msg_print_text(const struct printk_log *msg, bool syslog, char *bu
}
if (buf) {
- if (print_prefix(msg, syslog, NULL) +
+ if (print_prefix(msg, syslog, time, NULL) +
text_len + 1 >= size - len)
break;
- len += print_prefix(msg, syslog, buf + len);
+ len += print_prefix(msg, syslog, time, buf + len);
memcpy(buf + len, text, text_len);
len += text_len;
buf[len++] = '\n';
} else {
/* SYSLOG_ACTION_* buffer size only calculation */
- len += print_prefix(msg, syslog, NULL);
+ len += print_prefix(msg, syslog, time, NULL);
len += text_len;
len++;
}
@@ -1332,9 +1331,17 @@ static int syslog_print(char __user *buf, int size)
break;
}
+ /*
+ * To keep reading/counting partial line consistent,
+ * use printk_time value as of the beginning of a line.
+ */
+ if (!syslog_partial)
+ syslog_time = printk_time;
+
skip = syslog_partial;
msg = log_from_idx(syslog_idx);
- n = msg_print_text(msg, true, text, LOG_LINE_MAX + PREFIX_MAX);
+ n = msg_print_text(msg, true, syslog_time, text,
+ LOG_LINE_MAX + PREFIX_MAX);
if (n - syslog_partial <= size) {
/* message fits into buffer, move forward */
syslog_idx = log_next(syslog_idx);
@@ -1374,11 +1381,13 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
u64 next_seq;
u64 seq;
u32 idx;
+ bool time;
text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
if (!text)
return -ENOMEM;
+ time = printk_time;
logbuf_lock_irq();
/*
* Find first record that fits, including all following records,
@@ -1389,7 +1398,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
while (seq < log_next_seq) {
struct printk_log *msg = log_from_idx(idx);
- len += msg_print_text(msg, true, NULL, 0);
+ len += msg_print_text(msg, true, time, NULL, 0);
idx = log_next(idx);
seq++;
}
@@ -1400,7 +1409,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
while (len > size && seq < log_next_seq) {
struct printk_log *msg = log_from_idx(idx);
- len -= msg_print_text(msg, true, NULL, 0);
+ len -= msg_print_text(msg, true, time, NULL, 0);
idx = log_next(idx);
seq++;
}
@@ -1411,14 +1420,9 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
len = 0;
while (len >= 0 && seq < next_seq) {
struct printk_log *msg = log_from_idx(idx);
- int textlen;
+ int textlen = msg_print_text(msg, true, time, text,
+ LOG_LINE_MAX + PREFIX_MAX);
- textlen = msg_print_text(msg, true, text,
- LOG_LINE_MAX + PREFIX_MAX);
- if (textlen < 0) {
- len = textlen;
- break;
- }
idx = log_next(idx);
seq++;
@@ -1542,11 +1546,14 @@ int do_syslog(int type, char __user *buf, int len, int source)
} else {
u64 seq = syslog_seq;
u32 idx = syslog_idx;
+ bool time = syslog_partial ? syslog_time : printk_time;
while (seq < log_next_seq) {
struct printk_log *msg = log_from_idx(idx);
- error += msg_print_text(msg, true, NULL, 0);
+ error += msg_print_text(msg, true, time, NULL,
+ 0);
+ time = printk_time;
idx = log_next(idx);
seq++;
}
@@ -2004,6 +2011,7 @@ EXPORT_SYMBOL(printk);
#define LOG_LINE_MAX 0
#define PREFIX_MAX 0
+#define printk_time false
static u64 syslog_seq;
static u32 syslog_idx;
@@ -2027,8 +2035,8 @@ static void console_lock_spinning_enable(void) { }
static int console_lock_spinning_disable_and_check(void) { return 0; }
static void call_console_drivers(const char *ext_text, size_t ext_len,
const char *text, size_t len) {}
-static size_t msg_print_text(const struct printk_log *msg,
- bool syslog, char *buf, size_t size) { return 0; }
+static size_t msg_print_text(const struct printk_log *msg, bool syslog,
+ bool time, char *buf, size_t size) { return 0; }
static bool suppress_message_printing(int level) { return false; }
#endif /* CONFIG_PRINTK */
@@ -2386,8 +2394,7 @@ skip:
len += msg_print_text(msg,
console_msg_format & MSG_FORMAT_SYSLOG,
- text + len,
- sizeof(text) - len);
+ printk_time, text + len, sizeof(text) - len);
if (nr_ext_console_drivers) {
ext_len = msg_print_ext_header(ext_text,
sizeof(ext_text),
@@ -3111,7 +3118,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
goto out;
msg = log_from_idx(dumper->cur_idx);
- l = msg_print_text(msg, syslog, line, size);
+ l = msg_print_text(msg, syslog, printk_time, line, size);
dumper->cur_idx = log_next(dumper->cur_idx);
dumper->cur_seq++;
@@ -3182,6 +3189,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
u32 next_idx;
size_t l = 0;
bool ret = false;
+ bool time = printk_time;
if (!dumper->active)
goto out;
@@ -3205,7 +3213,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
while (seq < dumper->next_seq) {
struct printk_log *msg = log_from_idx(idx);
- l += msg_print_text(msg, true, NULL, 0);
+ l += msg_print_text(msg, true, time, NULL, 0);
idx = log_next(idx);
seq++;
}
@@ -3216,7 +3224,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
while (l > size && seq < dumper->next_seq) {
struct printk_log *msg = log_from_idx(idx);
- l -= msg_print_text(msg, true, NULL, 0);
+ l -= msg_print_text(msg, true, time, NULL, 0);
idx = log_next(idx);
seq++;
}
@@ -3229,7 +3237,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
while (seq < dumper->next_seq) {
struct printk_log *msg = log_from_idx(idx);
- l += msg_print_text(msg, syslog, buf + l, size - l);
+ l += msg_print_text(msg, syslog, time, buf + l, size - l);
idx = log_next(idx);
seq++;
}