[PATCH] vfs_getxattr_alloc(): don't allocate buf on failure

[Miklos Szeredi <mszeredi@redhat.com>]

Some callers of vfs_getxattr_alloc() assume that on failure the allocated
buffer does not need to be freed.

Callers could be fixed, but fixing the semantics of vfs_getxattr_alloc() is
simpler and makes sure that this class of bugs does not occur again.

Reported-and-tested-by: syzbot+942d5390db2d9624ced8@syzkaller.appspotmail.com
Fixes: 1601fbad2b14 ("xattr: define vfs_getxattr_alloc and vfs_xattr_cmp")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/xattr.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index e8dd03e4561e..1800cfa97411 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -383,7 +383,10 @@ vfs_getxattr_alloc(struct user_namespace *mnt_userns, struct dentry *dentry,
 	}
 
 	error = handler->get(handler, dentry, inode, name, value, error);
-	*xattr_value = value;
+	if (error < 0 && value != *xattr_value)
+		kfree(value);
+	else
+		*xattr_value = value;
 	return error;
 }
 
-- 
2.35.3