[PATCH] powerpc/pseries: add input size check in ofdt_write

[Miaoqian Lin]

A malicious user could pass an arbitrarily bad value
to memdup_user_nul(), potentially causing kernel crash.

This follows the same pattern as commit ee76746387f6
("netdevsim: prevent bad user input in nsim_dev_health_break_write()")

Found via static analysis and code review.

Fixes: 3783225130f0 ("powerpc/pseries: use memdup_user_nul")
Cc: stable at vger.kernel.org
Signed-off-by: Miaoqian Lin <linmq006 at gmail.com>
---
 arch/powerpc/platforms/pseries/reconfig.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/reconfig.c b/arch/powerpc/platforms/pseries/reconfig.c
index 599bd2c78514..b6bc1d8b2207 100644
--- a/arch/powerpc/platforms/pseries/reconfig.c
+++ b/arch/powerpc/platforms/pseries/reconfig.c
@@ -366,6 +366,9 @@ static ssize_t ofdt_write(struct file *file, const char __user *buf, size_t coun
 	if (rv)
 		return rv;
 
+	if (count == 0 || count > PAGE_SIZE)
+		return -EINVAL;
+
 	kbuf = memdup_user_nul(buf, count);
 	if (IS_ERR(kbuf))
 		return PTR_ERR(kbuf);
-- 
2.39.5 (Apple Git-154)