From e80c1a9d5f514ce5134c6c4263a11607341466c9 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Tue, 4 Dec 2018 19:00:01 +0900 Subject: [PATCH] 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 Cc: linux-kernel@vger.kernel.org Signed-off-by: Tetsuo Handa Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- kernel/printk/printk.c | 70 +++++++++++++++++++++++------------------- 1 file 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 @@ void console_unlock(void) 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++; }