[PATCH] xtensa: simdisk: add input size check in proc_write_simdisk

[Miaoqian Lin <linmq006@gmail.com>]

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()")

Fixes: b6c7e873daf7 ("xtensa: ISS: add host file-based simulated disk")
Fixes: 16e5c1fc3604 ("convert a bunch of open-coded instances of memdup_user_nul()")
Cc: stable@vger.kernel.org
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
---
 arch/xtensa/platforms/iss/simdisk.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/xtensa/platforms/iss/simdisk.c b/arch/xtensa/platforms/iss/simdisk.c
index 6ed009318d24..3cafc8feddee 100644
--- a/arch/xtensa/platforms/iss/simdisk.c
+++ b/arch/xtensa/platforms/iss/simdisk.c
@@ -231,10 +231,14 @@ static ssize_t proc_read_simdisk(struct file *file, char __user *buf,
 static ssize_t proc_write_simdisk(struct file *file, const char __user *buf,
 			size_t count, loff_t *ppos)
 {
-	char *tmp = memdup_user_nul(buf, count);
+	char *tmp;
 	struct simdisk *dev = pde_data(file_inode(file));
 	int err;
 
+	if (count == 0 || count > PAGE_SIZE)
+		return -EINVAL;
+
+	tmp = memdup_user_nul(buf, count);
 	if (IS_ERR(tmp))
 		return PTR_ERR(tmp);
 
-- 
2.35.1