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authorJan Beulich <JBeulich@suse.com>2012-06-22 15:36:09 (GMT)
committerAntti Palosaari <crope@iki.fi>2012-07-03 19:57:25 (GMT)
commitf29a0bf7f4fc22b624f6345b22dff4cc35674767 (patch)
tree97314f054e89e3ec980712d8c0e7885f0e8c1d20
parent4a4e01e5474395536c46d83d10918890f0f7f075 (diff)
syslog: fill buffer with more than a single message for SYSLOG_ACTION_READ
The recent changes to the printk buffer management resulted in SYSLOG_ACTION_READ to only return a single message, whereas previously the buffer would get filled as much as possible. As, when too small to fit everything, filling it to the last byte would be pretty ugly with the new code, the patch arranges for as many messages as possible to get returned in a single invocation. User space tools in at least all SLES versions depend on the old behavior. This at once addresses the issue attempted to get fixed with commit b56a39ac263e5b8cafedd551a49c2105e68b98c2 ("printk: return -EINVAL if the message len is bigger than the buf size"), and since that commit widened the possibility for losing a message altogether, the patch here assumes that this other commit would get reverted first (otherwise the patch here won't apply). Furthermore, this patch also addresses the problem dealt with in commit 4a77a5a06ec66ed05199b301e7c25f42f979afdc ("printk: use mutex lock to stop syslog_seq from going wild"), so I'd recommend reverting that one too (albeit there's no direct collision between the two). Signed-off-by: Jan Beulich <jbeulich@suse.com> Acked-by: Kay Sievers <kay@vrfy.org> Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/printk.c51
1 files changed, 37 insertions, 14 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index ff05361..cdfba44 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -862,26 +862,49 @@ static int syslog_print(char __user *buf, int size)
{
char *text;
struct log *msg;
- int len;
+ int len = 0;
text = kmalloc(LOG_LINE_MAX, GFP_KERNEL);
if (!text)
return -ENOMEM;
- raw_spin_lock_irq(&logbuf_lock);
- if (syslog_seq < log_first_seq) {
- /* messages are gone, move to first one */
- syslog_seq = log_first_seq;
- syslog_idx = log_first_idx;
- }
- msg = log_from_idx(syslog_idx);
- len = msg_print_text(msg, true, text, LOG_LINE_MAX);
- syslog_idx = log_next(syslog_idx);
- syslog_seq++;
- raw_spin_unlock_irq(&logbuf_lock);
+ while (size > 0) {
+ size_t n;
+
+ raw_spin_lock_irq(&logbuf_lock);
+ if (syslog_seq < log_first_seq) {
+ /* messages are gone, move to first one */
+ syslog_seq = log_first_seq;
+ syslog_idx = log_first_idx;
+ }
+ if (syslog_seq == log_next_seq) {
+ raw_spin_unlock_irq(&logbuf_lock);
+ break;
+ }
+ msg = log_from_idx(syslog_idx);
+ n = msg_print_text(msg, true, text, LOG_LINE_MAX);
+ if (n <= size) {
+ syslog_idx = log_next(syslog_idx);
+ syslog_seq++;
+ } else
+ n = 0;
+ raw_spin_unlock_irq(&logbuf_lock);
+
+ if (!n)
+ break;
- if (len > 0 && copy_to_user(buf, text, len))
- len = -EFAULT;
+ len += n;
+ size -= n;
+ buf += n;
+ n = copy_to_user(buf - n, text, n);
+
+ if (n) {
+ len -= n;
+ if (!len)
+ len = -EFAULT;
+ break;
+ }
+ }
kfree(text);
return len;

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