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printk: fix buffer overflow when calling log_prefix function from cal…
…l_console_drivers This patch corrects a buffer overflow in kernels from 3.0 to 3.4 when calling log_prefix() function from call_console_drivers(). This bug existed in previous releases but has been revealed with commit 162a7e7 (2.6.39 => 3.0) that made changes about how to allocate memory for early printk buffer (use of memblock_alloc). It disappears with commit 7ff9554 (3.4 => 3.5) that does a refactoring of printk buffer management. In log_prefix(), the access to "p", "p", "p" or "simple_strtoul(&p, &endp, 10)" may cause a buffer overflow as this function is called from call_console_drivers by passing "&LOG_BUF(cur_index)" where the index must be masked to do not exceed the buffer's boundary. The trick is to prepare in call_console_drivers() a buffer with the necessary data (PRI field of syslog message) to be safely evaluated in log_prefix(). This patch can be applied to stable kernel branches 3.0.y, 3.2.y and 3.4.y. Without this patch, one can freeze a server running this loop from shell : $ export DUMMY=`cat /dev/urandom | tr -dc '12345AZERTYUIOPQSDFGHJKLMWXCVBNazertyuiopqsdfghjklmwxcvbn' | head -c255` $ while true do ; echo $DUMMY > /dev/kmsg ; done The "server freeze" depends on where memblock_alloc does allocate printk buffer : if the buffer overflow is inside another kernel allocation the problem may not be revealed, else the server may hangs up. Signed-off-by: Alexandre SIMON <Alexandre.Simon@univ-lorraine.fr> Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>
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