cifs: fix memory leak in smb3_fs_context_parse_param error path

Add proper cleanup of ctx->source and fc->source to the
cifs_parse_mount_err error handler. This ensures that memory allocated
for the source strings is correctly freed on all error paths, matching
the cleanup already performed in the success path by
smb3_cleanup_fs_context_contents().
Pointers are also set to NULL after freeing to prevent potential
double-free issues.

This change fixes a memory leak originally detected by syzbot. The
leak occurred when processing Opt_source mount options if an error
happened after ctx->source and fc->source were successfully
allocated but before the function completed.

The specific leak sequence was:
1. ctx->source = smb3_fs_context_fullpath(ctx, '/') allocates memory
2. fc->source = kstrdup(ctx->source, GFP_KERNEL) allocates more memory
3. A subsequent error jumps to cifs_parse_mount_err
4. The old error handler freed passwords but not the source strings,
causing the memory to leak.

This issue was not addressed by commit e8c73eb ("cifs: client:
fix memory leak in smb3_fs_context_parse_param"), which only fixed
leaks from repeated fsconfig() calls but not this error path.

Patch updated with minor change suggested by kernel test robot

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=87be6809ed9bf6d718e3
Fixes: 24e0a1e ("cifs: switch to new mount api")
Reviewed-by: David Howells <[email protected]>
Signed-off-by: Shaurya Rane <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: shauryarane05

fs/smb/client/fs_context.c

@@ -1834,6 +1834,10 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 	ctx->password = NULL;
 	kfree_sensitive(ctx->password2);
 	ctx->password2 = NULL;
+	kfree(ctx->source);
+	ctx->source = NULL;
+	kfree(fc->source);
+	fc->source = NULL;
 	return -EINVAL;
 }