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@xxxxxxxxxxxxxxx>
Fixes: ba82664c134ef ("intel_th: Add Memory Storage Unit driver")
Cc: stable@xxxxxxxxxxxxxxx # 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);
--
2.19.2
