linux-kernel - Re: [PATCH] btrfs: Fix memory leak in __add_inode

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Date:   Thu, 9 Dec 2021 16:39:37 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Jianglei Nie <niejianglei2021@....com>, clm@...com,
        josef@...icpanda.com, dsterba@...e.com
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Fix memory leak in __add_inode_ref()



On 2021/12/9 14:56, Jianglei Nie wrote:
> Line 1169 (#3) allocates a memory chunk for victim_name by kmalloc(),
> but  when the function returns in line 1184 (#4) victim_name allcoated
> by line 1169 (#3) is not freed, which will lead to a memory leak.
> There is a similar snippet of code in this function as allocating a memory
> chunk for victim_name in line 1104 (#1) as well as releasing the memory
> in line 1116 (#2).
>
> We should kfree() victim_name when the return value of backref_in_log()
> is less than zero and before the function returns in line 1184 (#4).
>
> 1057 static inline int __add_inode_ref(struct btrfs_trans_handle *trans,
> 1058 				  struct btrfs_root *root,
> 1059 				  struct btrfs_path *path,
> 1060 				  struct btrfs_root *log_root,
> 1061 				  struct btrfs_inode *dir,
> 1062 				  struct btrfs_inode *inode,
> 1063 				  u64 inode_objectid, u64 parent_objectid,
> 1064 				  u64 ref_index, char *name, int namelen,
> 1065 				  int *search_done)
> 1066 {
>
> 1104 	victim_name = kmalloc(victim_name_len, GFP_NOFS);
> 	// #1: kmalloc (victim_name-1)
> 1105 	if (!victim_name)
> 1106 		return -ENOMEM;
>
> 1112	ret = backref_in_log(log_root, &search_key,
> 1113			parent_objectid, victim_name,
> 1114			victim_name_len);
> 1115	if (ret < 0) {
> 1116		kfree(victim_name); // #2: kfree (victim_name-1)
> 1117		return ret;
> 1118	} else if (!ret) {
>
> 1169 	victim_name = kmalloc(victim_name_len, GFP_NOFS);
> 	// #3: kmalloc (victim_name-2)
> 1170 	if (!victim_name)
> 1171 		return -ENOMEM;
>
> 1180 	ret = backref_in_log(log_root, &search_key,
> 1181 			parent_objectid, victim_name,
> 1182 			victim_name_len);
> 1183 	if (ret < 0) {
> 1184 		return ret; // #4: missing kfree (victim_name-2)
> 1185 	} else if (!ret) {
>
> 1241 	return 0;
> 1242 }
>
> Signed-off-by: Jianglei Nie <niejianglei2021@....com>

Reviewed-by: Qu Wenruo <wqu@...e.com>

BTW, mind to share the way how you exposed the missing kfree()?

Some awesome static analyse tool or just by eyeballing?

Thanks,
Qu
> ---
>   fs/btrfs/tree-log.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 8ab33caf016f..d373fec55521 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -1181,6 +1181,7 @@ static inline int __add_inode_ref(struct btrfs_trans_handle *trans,
>   					     parent_objectid, victim_name,
>   					     victim_name_len);
>   			if (ret < 0) {
> +				kfree(victim_name);
>   				return ret;
>   			} else if (!ret) {
>   				ret = -ENOENT;
>