[PATCH] btrfs: fix oob Read in getname_kernel

[Edward Adam Davis]

If ioctl does not pass in the correct tgtdev_name string, oob will occur because
"\0" cannot be found.

Reported-and-tested-by: syzbot+33f23b49ac24f986c9e8@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 fs/btrfs/dev-replace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index f9544fda38e9..e7e96e57f682 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -730,7 +730,7 @@ static int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 int btrfs_dev_replace_by_ioctl(struct btrfs_fs_info *fs_info,
 			    struct btrfs_ioctl_dev_replace_args *args)
 {
-	int ret;
+	int ret, len;
 
 	switch (args->start.cont_reading_from_srcdev_mode) {
 	case BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_ALWAYS:
@@ -740,8 +740,10 @@ int btrfs_dev_replace_by_ioctl(struct btrfs_fs_info *fs_info,
 		return -EINVAL;
 	}
 
+	len = strnlen(args->start.tgtdev_name, BTRFS_DEVICE_PATH_NAME_MAX + 1);
 	if ((args->start.srcdevid == 0 && args->start.srcdev_name[0] == '\0') ||
-	    args->start.tgtdev_name[0] == '\0')
+	    args->start.tgtdev_name[0] == '\0' ||
+	    len == BTRFS_DEVICE_PATH_NAME_MAX + 1)
 		return -EINVAL;
 
 	ret = btrfs_dev_replace_start(fs_info, args->start.tgtdev_name,
-- 
2.43.0