3.13-stable review patch. If anyone has any objections, please let me know.
------------------ From: Linus Torvalds <[email protected]> commit e4178d809fdaee32a56833fff1f5056c99e90a1a upstream. This is not a buffer overflow in the traditional sense: we don't overflow any *kernel* buffers, but we do mis-count the amount of data we copy back to user space for the SYSLOG_ACTION_READ_ALL case. In particular, if the user buffer is too small to hold everything, and *if* there is a continuation line at just the right place, we can end up giving the user more data than he asked for. The reason is that we first count up the number of bytes all the log records contains, then we walk the records again until we've skipped the records at the beginning that won't fit, and then we walk the rest of the records and copy them to the user space buffer. And in between that "skip the initial records that won't fit" and the "copy the records that *will* fit to user space", we reset the 'prev' variable that contained the record information for the last record not copied. That meant that when we started copying to user space, we now had a different character count than what we had originally calculated in the first record walk-through. The fix is to simply not clear the 'prev' flags value (in both cases where we had the same logic: syslog_print_all and kmsg_dump_get_buffer: the latter is used for pstore-like dumping) Reported-and-tested-by: Debabrata Banerjee <[email protected]> Acked-by: Kay Sievers <[email protected]> Cc: Jeff Mahoney <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Cc: Josh Hunt <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/printk/printk.c | 2 -- 1 file changed, 2 deletions(-) --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1080,7 +1080,6 @@ static int syslog_print_all(char __user next_seq = log_next_seq; len = 0; - prev = 0; while (len >= 0 && seq < next_seq) { struct printk_log *msg = log_from_idx(idx); int textlen; @@ -2789,7 +2788,6 @@ bool kmsg_dump_get_buffer(struct kmsg_du next_idx = idx; l = 0; - prev = 0; while (seq < dumper->next_seq) { struct printk_log *msg = log_from_idx(idx); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
