[PATCH 5.4 225/389] s390/zcore: fix race when reading from hardware system area

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>

[ Upstream commit 9ffed254d938c9e99eb7761c7f739294c84e0367 ]

Memory buffer used for reading out data from hardware system
area is not protected against concurrent access.

Reported-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Fixes: 411ed3225733 ("[S390] zfcpdump support.")
Acked-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Tested-by: Alexander Egorenkov <egorenar@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/e68137f0f9a0d2558f37becc20af18e2939934f6.1658206891.git.agordeev@xxxxxxxxxxxxx
Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/s390/char/zcore.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/char/zcore.c b/drivers/s390/char/zcore.c
index 08f812475f5e..c9d172510509 100644
--- a/drivers/s390/char/zcore.c
+++ b/drivers/s390/char/zcore.c
@@ -53,6 +53,7 @@ static struct dentry *zcore_reipl_file;
 static struct dentry *zcore_hsa_file;
 static struct ipl_parameter_block *zcore_ipl_block;
 
+static DEFINE_MUTEX(hsa_buf_mutex);
 static char hsa_buf[PAGE_SIZE] __aligned(PAGE_SIZE);
 
 /*
@@ -69,19 +70,24 @@ int memcpy_hsa_user(void __user *dest, unsigned long src, size_t count)
 	if (!hsa_available)
 		return -ENODATA;
 
+	mutex_lock(&hsa_buf_mutex);
 	while (count) {
 		if (sclp_sdias_copy(hsa_buf, src / PAGE_SIZE + 2, 1)) {
 			TRACE("sclp_sdias_copy() failed\n");
+			mutex_unlock(&hsa_buf_mutex);
 			return -EIO;
 		}
 		offset = src % PAGE_SIZE;
 		bytes = min(PAGE_SIZE - offset, count);
-		if (copy_to_user(dest, hsa_buf + offset, bytes))
+		if (copy_to_user(dest, hsa_buf + offset, bytes)) {
+			mutex_unlock(&hsa_buf_mutex);
 			return -EFAULT;
+		}
 		src += bytes;
 		dest += bytes;
 		count -= bytes;
 	}
+	mutex_unlock(&hsa_buf_mutex);
 	return 0;
 }
 
@@ -99,9 +105,11 @@ int memcpy_hsa_kernel(void *dest, unsigned long src, size_t count)
 	if (!hsa_available)
 		return -ENODATA;
 
+	mutex_lock(&hsa_buf_mutex);
 	while (count) {
 		if (sclp_sdias_copy(hsa_buf, src / PAGE_SIZE + 2, 1)) {
 			TRACE("sclp_sdias_copy() failed\n");
+			mutex_unlock(&hsa_buf_mutex);
 			return -EIO;
 		}
 		offset = src % PAGE_SIZE;
@@ -111,6 +119,7 @@ int memcpy_hsa_kernel(void *dest, unsigned long src, size_t count)
 		dest += bytes;
 		count -= bytes;
 	}
+	mutex_unlock(&hsa_buf_mutex);
 	return 0;
 }
 
-- 
2.35.1