Re: [PATCH] bcachefs: fix memleak in bch2_split_devs

[Brian Foster <bfoster@redhat.com>]

On Sun, Jan 07, 2024 at 03:05:59PM +0800, Su Yue wrote:
> The pointer dev_name can be modified by strseq(),
> then causes the memleak:
> 
> unreferenced object 0xffff9d08a2916c80 (size 32):
>   comm "mount.bcachefs", pid 9090, jiffies 4295856224 (age 17.564s)
>   hex dump (first 32 bytes):
>     2f 64 65 76 2f 6d 61 70 70 65 72 2f 74 65 73 74  /dev/mapper/test
>     2d 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00  -0..............
>   backtrace:
>     [<00000000c5d3be7d>] __kmem_cache_alloc_node+0x1f3/0x2c0
>     [<0000000052215d26>] __kmalloc_node_track_caller+0x51/0x150
>     [<0000000069fea956>] kstrdup+0x32/0x60
>     [<000000000877fcf1>] bch2_split_devs+0x3f/0x150 [bcachefs]
>     [<000000007ee93204>] bch2_mount+0xcb/0x640 [bcachefs]
>     [<000000002dd1e04b>] legacy_get_tree+0x30/0x60
>     [<000000006afc31d3>] vfs_get_tree+0x28/0xf0
>     [<000000007b0c538e>] path_mount+0x475/0xb60
>     [<0000000092de5882>] __x64_sys_mount+0x105/0x140
>     [<0000000054fc05d8>] do_syscall_64+0x42/0xf0
>     [<00000000df584910>] entry_SYSCALL_64_after_hwframe+0x6e/0x76
> 
> Fix it by copying pointer dev_name at beginning then freeing the copied
> pointer at end.
> 
> Signed-off-by: Su Yue <glass.su@suse.com>
> ---
>  fs/bcachefs/util.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/bcachefs/util.c b/fs/bcachefs/util.c
> index c2ef7cddaa4f..789953c14f55 100644
> --- a/fs/bcachefs/util.c
> +++ b/fs/bcachefs/util.c
> @@ -1186,7 +1186,9 @@ int bch2_split_devs(const char *_dev_name, darray_str *ret)
>  {
>  	darray_init(ret);
>  
> -	char *dev_name = kstrdup(_dev_name, GFP_KERNEL), *s = dev_name;
> +	char *dev_name = kstrdup(_dev_name, GFP_KERNEL);
> +	char *s = dev_name, *orig = dev_name;
> +

Thanks for the patch. I see this is just moving the assignment of *s,
but there's no need for that assignment in this code, right? If not, I
think this would look a little bit cleaner if it fixed that up as well.
I.e., something like:

	char *s, *dev_name, *orig;

	dev_name = orig = kstrdup(_dev_name, GFP_KERNEL);
>  	if (!dev_name)
>  		return -ENOMEM;
>  

... and then otherwise the rest LGTM.

Brian

> @@ -1201,10 +1203,10 @@ int bch2_split_devs(const char *_dev_name, darray_str *ret)
>  		}
>  	}
>  
> -	kfree(dev_name);
> +	kfree(orig);
>  	return 0;
>  err:
>  	bch2_darray_str_exit(ret);
> -	kfree(dev_name);
> +	kfree(orig);
>  	return -ENOMEM;
>  }
> -- 
> 2.43.0
> 
>