unsigned numbers in the ring-buffer code.
https://bugzilla.kernel.org/show_bug.cgi?id=118001
At first I did not think this was too much of an issue, because the
overflow would be caught later when either too much data was allocated
or it would trigger RB_WARN_ON() which shuts down the ring buffer.
But looking closer into it, I found that the right settings could bypass
the checks and crash the kernel. Luckily, this is only accessible
by root.
The first fix is to convert all the variables into long, such that
we don't get into issues between 32 bit variables being assigned 64 bit
ones. This fixes the RB_WARN_ON() triggering.
The next fix is to get rid of a duplicate DIV_ROUND_UP() that when called
twice with the right value, can cause a kernel crash.
The first DIV_ROUND_UP() is to normalize the input and it is checked
against the minimum allowable value. But then DIV_ROUND_UP() is called
again, which can overflow due to the (a + b - 1)/b, logic. The first
called upped the value, the second can overflow (with the +b part).
The second call to DIV_ROUND_UP() came in via a second change a while ago
and the code is cleaned up to remove it.
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Merge tag 'trace-fixes-v4.6-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing ring-buffer fixes from Steven Rostedt:
"Hao Qin reported an integer overflow possibility with signed and
unsigned numbers in the ring-buffer code.
https://bugzilla.kernel.org/show_bug.cgi?id=118001
At first I did not think this was too much of an issue, because the
overflow would be caught later when either too much data was allocated
or it would trigger RB_WARN_ON() which shuts down the ring buffer.
But looking closer into it, I found that the right settings could
bypass the checks and crash the kernel. Luckily, this is only
accessible by root.
The first fix is to convert all the variables into long, such that we
don't get into issues between 32 bit variables being assigned 64 bit
ones. This fixes the RB_WARN_ON() triggering.
The next fix is to get rid of a duplicate DIV_ROUND_UP() that when
called twice with the right value, can cause a kernel crash.
The first DIV_ROUND_UP() is to normalize the input and it is checked
against the minimum allowable value. But then DIV_ROUND_UP() is
called again, which can overflow due to the (a + b - 1)/b, logic. The
first called upped the value, the second can overflow (with the +b
part).
The second call to DIV_ROUND_UP() came in via a second change a while
ago and the code is cleaned up to remove it"
* tag 'trace-fixes-v4.6-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
ring-buffer: Prevent overflow of size in ring_buffer_resize()
ring-buffer: Use long for nr_pages to avoid overflow failures
2fe2edf85f