Commit eb02dac9 authored by Kay Sievers's avatar Kay Sievers Committed by Greg Kroah-Hartman

kmsg: /proc/kmsg - support reading of partial log records

Restore support for partial reads of any size on /proc/kmsg, in case the
supplied read buffer is smaller than the record size.

Some people seem to think is is ia good idea to run:
  $ dd if=/proc/kmsg bs=1 of=...
as a klog bridge.

Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=44211Reported-by: default avatarJukka Ollila <jiiksteri@gmail.com>
Signed-off-by: default avatarKay Sievers <kay@vrfy.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 68b6507d
...@@ -217,6 +217,7 @@ static DEFINE_RAW_SPINLOCK(logbuf_lock); ...@@ -217,6 +217,7 @@ static DEFINE_RAW_SPINLOCK(logbuf_lock);
/* the next printk record to read by syslog(READ) or /proc/kmsg */ /* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq; static u64 syslog_seq;
static u32 syslog_idx; static u32 syslog_idx;
static size_t syslog_partial;
/* index and sequence number of the first record stored in the buffer */ /* index and sequence number of the first record stored in the buffer */
static u64 log_first_seq; static u64 log_first_seq;
...@@ -890,22 +891,33 @@ static int syslog_print(char __user *buf, int size) ...@@ -890,22 +891,33 @@ static int syslog_print(char __user *buf, int size)
while (size > 0) { while (size > 0) {
size_t n; size_t n;
size_t skip;
raw_spin_lock_irq(&logbuf_lock); raw_spin_lock_irq(&logbuf_lock);
if (syslog_seq < log_first_seq) { if (syslog_seq < log_first_seq) {
/* messages are gone, move to first one */ /* messages are gone, move to first one */
syslog_seq = log_first_seq; syslog_seq = log_first_seq;
syslog_idx = log_first_idx; syslog_idx = log_first_idx;
syslog_partial = 0;
} }
if (syslog_seq == log_next_seq) { if (syslog_seq == log_next_seq) {
raw_spin_unlock_irq(&logbuf_lock); raw_spin_unlock_irq(&logbuf_lock);
break; break;
} }
skip = syslog_partial;
msg = log_from_idx(syslog_idx); msg = log_from_idx(syslog_idx);
n = msg_print_text(msg, true, text, LOG_LINE_MAX); n = msg_print_text(msg, true, text, LOG_LINE_MAX);
if (n <= size) { if (n - syslog_partial <= size) {
/* message fits into buffer, move forward */
syslog_idx = log_next(syslog_idx); syslog_idx = log_next(syslog_idx);
syslog_seq++; syslog_seq++;
n -= syslog_partial;
syslog_partial = 0;
} else if (!len){
/* partial read(), remember position */
n = size;
syslog_partial += n;
} else } else
n = 0; n = 0;
raw_spin_unlock_irq(&logbuf_lock); raw_spin_unlock_irq(&logbuf_lock);
...@@ -913,17 +925,15 @@ static int syslog_print(char __user *buf, int size) ...@@ -913,17 +925,15 @@ static int syslog_print(char __user *buf, int size)
if (!n) if (!n)
break; break;
len += n; if (copy_to_user(buf, text + skip, n)) {
size -= n;
buf += n;
n = copy_to_user(buf - n, text, n);
if (n) {
len -= n;
if (!len) if (!len)
len = -EFAULT; len = -EFAULT;
break; break;
} }
len += n;
size -= n;
buf += n;
} }
kfree(text); kfree(text);
...@@ -1107,6 +1117,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file) ...@@ -1107,6 +1117,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
/* messages are gone, move to first one */ /* messages are gone, move to first one */
syslog_seq = log_first_seq; syslog_seq = log_first_seq;
syslog_idx = log_first_idx; syslog_idx = log_first_idx;
syslog_partial = 0;
} }
if (from_file) { if (from_file) {
/* /*
...@@ -1129,6 +1140,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file) ...@@ -1129,6 +1140,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
idx = log_next(idx); idx = log_next(idx);
seq++; seq++;
} }
error -= syslog_partial;
} }
raw_spin_unlock_irq(&logbuf_lock); raw_spin_unlock_irq(&logbuf_lock);
break; break;
......
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