linux-kernel - Re: memory leak in generic_parse

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1030308.1607468099@warthog.procyon.org.uk>
Date:   Tue, 08 Dec 2020 22:54:59 +0000
From:   David Howells <dhowells@...hat.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     dhowells@...hat.com,
        syzbot <syzbot+86dc6632faaca40133ab@...kaller.appspotmail.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: memory leak in generic_parse_monolithic [+PATCH]

Randy Dunlap <rdunlap@...radead.org> 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?

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;