Re: memory leak in generic_parse_monolithic [+PATCH]

[Randy Dunlap]

On 12/8/20 2:54 PM, David Howells wrote:
> Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
> 
>>> Now the backtrace only shows what the state was when the string was allocated;
>>> it doesn't show what happened to it after that, so another possibility is that
>>> the filesystem being mounted nicked what vfs_parse_fs_param() had rightfully
>>> stolen, transferring fc->source somewhere else and then failed to release it -
>>> most likely on mount failure (ie. it's an error handling bug in the
>>> filesystem).
>>>
>>> Do we know what filesystem it was?
>>
>> Yes, it's call AFS (or kAFS).
> 
> Hmmm...  afs parses the string in afs_parse_source() without modifying it,
> then moves the pointer to fc->source (parallelling vfs_parse_fs_param()) and
> doesn't touch it again.  fc->source should be cleaned up by do_new_mount()
> calling put_fs_context() at the end of the function.
> 
> As far as I can tell with the attached print-insertion patch, it works, called
> by the following commands, some of which are correct and some which aren't:
> 
> # mount -t afs none /xfstest.test/ -o dyn
> # umount /xfstest.test 
> # mount -t afs "" /xfstest.test/ -o foo
> mount: /xfstest.test: bad option; for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount.<type> helper program.
> # umount /xfstest.test 
> umount: /xfstest.test: not mounted.
> # mount -t afs %xfstest.test20 /xfstest.test/ -o foo
> mount: /xfstest.test: bad option; for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount.<type> helper program.
> # umount /xfstest.test 
> umount: /xfstest.test: not mounted.
> # mount -t afs %xfstest.test20 /xfstest.test/ 
> # umount /xfstest.test 
> 
> Do you know if the mount was successful and what the mount parameters were?

Here's the syzbot reproducer:
https://syzkaller.appspot.com/x/repro.c?x=129ca3d6500000

The "interesting" mount params are:
	source=%^]$[+%](${:\017k[)-:,source=%^]$[+.](%{:\017\200[)-:,\000

There is no other AFS activity: nothing mounted, no cells known (or
whatever that is), etc.

I don't recall if the mount was successful and I can't test it just now.
My laptop is mucked up.


Be aware that this report could just be a false positive: it waits
for 5 seconds then looks for a memleak. AFAIK, it's possible that the "leaked"
memory is still in valid use and will be freed some day.


> David
> ---
> diff --git a/fs/afs/super.c b/fs/afs/super.c
> index 6c5900df6aa5..4c44ec0196c9 100644
> --- a/fs/afs/super.c
> +++ b/fs/afs/super.c
> @@ -299,7 +299,7 @@ static int afs_parse_source(struct fs_context *fc, struct fs_parameter *param)
>  		ctx->cell = cell;
>  	}
>  
> -	_debug("CELL:%s [%p] VOLUME:%*.*s SUFFIX:%s TYPE:%d%s",
> +	kdebug("CELL:%s [%p] VOLUME:%*.*s SUFFIX:%s TYPE:%d%s",
>  	       ctx->cell->name, ctx->cell,
>  	       ctx->volnamesz, ctx->volnamesz, ctx->volname,
>  	       suffix ?: "-", ctx->type, ctx->force ? " FORCE" : "");
> @@ -318,6 +318,8 @@ static int afs_parse_param(struct fs_context *fc, struct fs_parameter *param)
>  	struct afs_fs_context *ctx = fc->fs_private;
>  	int opt;
>  
> +	kenter("%s,%p '%s'", param->key, param->string, param->string);
> +
>  	opt = fs_parse(fc, afs_fs_parameters, param, &result);
>  	if (opt < 0)
>  		return opt;
> diff --git a/fs/fs_context.c b/fs/fs_context.c
> index 2834d1afa6e8..f530a33876ce 100644
> --- a/fs/fs_context.c
> +++ b/fs/fs_context.c
> @@ -450,6 +450,8 @@ void put_fs_context(struct fs_context *fc)
>  	put_user_ns(fc->user_ns);
>  	put_cred(fc->cred);
>  	put_fc_log(fc);
> +	if (strcmp(fc->fs_type->name, "afs") == 0)
> +		printk("PUT %p '%s'\n", fc->source, fc->source);
>  	put_filesystem(fc->fs_type);
>  	kfree(fc->source);
>  	kfree(fc);
> @@ -671,6 +673,8 @@ void vfs_clean_context(struct fs_context *fc)
>  	fc->s_fs_info = NULL;
>  	fc->sb_flags = 0;
>  	security_free_mnt_opts(&fc->security);
> +	if (strcmp(fc->fs_type->name, "afs") == 0)
> +		printk("CLEAN %p '%s'\n", fc->source, fc->source);
>  	kfree(fc->source);
>  	fc->source = NULL;
>  
> 

I'll check more after my test machine is working again.

thanks.
-- 
~Randy