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printk: Fix calculation of length used to discard records

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While tracking down a weird buffer overflow issue in a program that
looked to be sane, I started double checking the length returned by
syslog(SYSLOG_ACTION_READ_ALL, ...) to make sure it wasn't overflowing
the buffer.

Sure enough, it was.  I saw this in strace:

  11339 syslog(SYSLOG_ACTION_READ_ALL, "<5>[244017.708129] REISERFS (dev"..., 8192) = 8279

It turns out that the loops that calculate how much space the entries
will take when they're copied don't include the newlines and prefixes
that will be included in the final output since prev flags is passed as
zero.

This patch properly accounts for it and fixes the overflow.

CC: stable@kernel.org
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jeff Mahoney 2012-08-10 15:07:09 -04:00 committed by Linus Torvalds
parent f4ba394c1b
commit e3756477ae
1 changed files with 2 additions and 0 deletions
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2
kernel/printk.c
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@ -1034,6 +1034,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
struct log *msg = log_from_idx(idx); struct log *msg = log_from_idx(idx);
len += msg_print_text(msg, prev, true, NULL, 0); len += msg_print_text(msg, prev, true, NULL, 0);
prev = msg->flags;
idx = log_next(idx); idx = log_next(idx);
seq++; seq++;
} }
@ -1046,6 +1047,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
struct log *msg = log_from_idx(idx); struct log *msg = log_from_idx(idx);
len -= msg_print_text(msg, prev, true, NULL, 0); len -= msg_print_text(msg, prev, true, NULL, 0);
prev = msg->flags;
idx = log_next(idx); idx = log_next(idx);
seq++; seq++;
} }