[PATCH] cifs: client: fix memory leak in smb3_fs_context_parse_param

[Edward Adam Davis <eadavis@qq.com>]

The user calls fsconfig twice, but when the program exits, free() only
frees ctx->source for the second fsconfig, not the first.
Regarding fc->source, there is no code in the fs context related to its
memory reclamation.

To fix this memory leak, release the source memory corresponding to ctx
or fc before each parsing.

syzbot reported:
BUG: memory leak
unreferenced object 0xffff888128afa360 (size 96):
  backtrace (crc 79c9c7ba):
    kstrdup+0x3c/0x80 mm/util.c:84
    smb3_fs_context_parse_param+0x229b/0x36c0 fs/smb/client/fs_context.c:1444

BUG: memory leak
unreferenced object 0xffff888112c7d900 (size 96):
  backtrace (crc 79c9c7ba):
    smb3_fs_context_fullpath+0x70/0x1b0 fs/smb/client/fs_context.c:629
    smb3_fs_context_parse_param+0x2266/0x36c0 fs/smb/client/fs_context.c:1438

Reported-by: syzbot+72afd4c236e6bc3f4bac@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=72afd4c236e6bc3f4bac
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/smb/client/fs_context.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index e60927b2a7c8..0e1949bcd6ea 100644
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -1435,12 +1435,14 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 			cifs_errorf(fc, "Unknown error parsing devname\n");
 			goto cifs_parse_mount_err;
 		}
+		kfree(ctx->source);
 		ctx->source = smb3_fs_context_fullpath(ctx, '/');
 		if (IS_ERR(ctx->source)) {
 			ctx->source = NULL;
 			cifs_errorf(fc, "OOM when copying UNC string\n");
 			goto cifs_parse_mount_err;
 		}
+		kfree(fc->source);
 		fc->source = kstrdup(ctx->source, GFP_KERNEL);
 		if (fc->source == NULL) {
 			cifs_errorf(fc, "OOM when copying UNC string\n");
-- 
2.43.0