linux-kernel - [PATCH 5.4 056/111] hostfs: fix memory handling in follow

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Message-Id: <20210412084006.133788036@linuxfoundation.org>
Date:   Mon, 12 Apr 2021 10:40:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 056/111] hostfs: fix memory handling in follow_link()

From: Al Viro <viro@...iv.linux.org.uk>

[ Upstream commit 7f6c411c9b50cfab41cc798e003eff27608c7016 ]

1) argument should not be freed in any case - the caller already has
it as ->s_fs_info (and uses it a lot afterwards)
2) allocate readlink buffer with kmalloc() - the caller has no way
to tell if it's got that (on absolute symlink) or a result of
kasprintf().  Sure, for SLAB and SLUB kfree() works on results of
kmem_cache_alloc(), but that's not documented anywhere, might change
in the future *and* is already not true for SLOB.

Fixes: 52b209f7b848 ("get rid of hostfs_read_inode()")
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/hostfs/hostfs_kern.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 4f5d857f6ecb..58a972667bf8 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -142,7 +142,7 @@ static char *follow_link(char *link)
 	char *name, *resolved, *end;
 	int n;
 
-	name = __getname();
+	name = kmalloc(PATH_MAX, GFP_KERNEL);
 	if (!name) {
 		n = -ENOMEM;
 		goto out_free;
@@ -171,12 +171,11 @@ static char *follow_link(char *link)
 		goto out_free;
 	}
 
-	__putname(name);
-	kfree(link);
+	kfree(name);
 	return resolved;
 
  out_free:
-	__putname(name);
+	kfree(name);
 	return ERR_PTR(n);
 }
 
-- 
2.30.2