The 'nr_pages' attribute of the 'msc' subdevices parses a comma-separated list of window sizes, passed from userspace. However, there is a bug in the string parsing logic wherein it doesn't exclude the comma character from the range of characters as it consumes them. This leads to an out-of-bounds access given a sufficiently long list. For example:

# echo 8,8,8,8 > /sys/bus/intel_th/devices/0-msc0/nr_pages

BUG: KASAN: slab-out-of-bounds in memchr+0x1e/0x40 Read of size 1 at addr ffff8803ffcebcd1 by task sh/825

CPU: 3 PID: 825 Comm: npktest.sh Tainted: G W 4.20.0-rc1+ Call Trace: dump_stack+0x7c/0xc0 print_address_description+0x6c/0x23c ? memchr+0x1e/0x40 kasan_report.cold.5+0x241/0x308 memchr+0x1e/0x40 nr_pages_store+0x203/0xd00 [intel_th_msu]

Fix this by accounting for the comma character.

Signed-off-by: Alexander Shishkin alexander.shishkin@linux.intel.com Fixes: ba82664c134ef ("intel_th: Add Memory Storage Unit driver") Cc: stable@vger.kernel.org # v4.4+ --- drivers/hwtracing/intel_th/msu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/intel_th/msu.c b/drivers/hwtracing/intel_th/msu.c index d293e55553bd..ba7aaf421f36 100644 --- a/drivers/hwtracing/intel_th/msu.c +++ b/drivers/hwtracing/intel_th/msu.c @@ -1423,7 +1423,8 @@ nr_pages_store(struct device *dev, struct device_attribute *attr, if (!end) break;

- len -= end - p; + /* consume the number and the following comma, hence +1 */ + len -= end - p + 1; p = end + 1; } while (len);