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fuse: always initialize sb->s_fs_info

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Syzkaller reports a null pointer dereference in fuse_test_super() that is
caused by sb->s_fs_info being NULL.

This is due to the fact that fuse_fill_super() is initializing s_fs_info,
which is too late, it's already on the fs_supers list.  The initialization
needs to be done in sget_fc() with the sb_lock held.

Move allocation of fuse_mount and fuse_conn from fuse_fill_super() into
fuse_get_tree().

After this ->kill_sb() will always be called with non-NULL ->s_fs_info,
hence fuse_mount_destroy() can drop the test for non-NULL "fm".

Reported-by: syzbot+74a15f02ccb51f398601@syzkaller.appspotmail.com
Fixes: 5d5b74aa9c ("fuse: allow sharing existing sb")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2021-10-21 10:01:39 +02:00
parent c191cd07ee
commit 80019f1138
1 changed files with 25 additions and 25 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

50
fs/fuse/inode.c
View file

@ -1557,8 +1557,6 @@ static int fuse_fill_super(struct super_block *sb, struct fs_context *fsc)
{
struct fuse_fs_context *ctx = fsc->fs_private;
int err;
struct fuse_conn *fc;
struct fuse_mount *fm;
if (!ctx->file || !ctx->rootmode_present ||
!ctx->user_id_present || !ctx->group_id_present)
@ -1574,22 +1572,6 @@ static int fuse_fill_super(struct super_block *sb, struct fs_context *fsc)
goto err;
ctx->fudptr = &ctx->file->private_data;
fc = kmalloc(sizeof(*fc), GFP_KERNEL);
err = -ENOMEM;
if (!fc)
goto err;
fm = kzalloc(sizeof(*fm), GFP_KERNEL);
if (!fm) {
kfree(fc);
goto err;
}
fuse_conn_init(fc, fm, sb->s_user_ns, &fuse_dev_fiq_ops, NULL);
fc->release = fuse_free_conn;
sb->s_fs_info = fm;
err = fuse_fill_super_common(sb, ctx);
if (err)
goto err;
@ -1621,22 +1603,40 @@ static int fuse_get_tree(struct fs_context *fsc)
{
struct fuse_fs_context *ctx = fsc->fs_private;
struct fuse_dev *fud;
struct fuse_conn *fc;
struct fuse_mount *fm;
struct super_block *sb;
int err;
fc = kmalloc(sizeof(*fc), GFP_KERNEL);
if (!fc)
return -ENOMEM;
fm = kzalloc(sizeof(*fm), GFP_KERNEL);
if (!fm) {
kfree(fc);
return -ENOMEM;
}
fuse_conn_init(fc, fm, fsc->user_ns, &fuse_dev_fiq_ops, NULL);
fc->release = fuse_free_conn;
fsc->s_fs_info = fm;
if (ctx->fd_present)
ctx->file = fget(ctx->fd);
if (IS_ENABLED(CONFIG_BLOCK) && ctx->is_bdev) {
err = get_tree_bdev(fsc, fuse_fill_super);
goto out_fput;
goto out;
}
/*
* While block dev mount can be initialized with a dummy device fd
* (found by device name), normal fuse mounts can't
*/
err = -EINVAL;
if (!ctx->file)
return -EINVAL;
goto out;
/*
* Allow creating a fuse mount with an already initialized fuse
@ -1652,7 +1652,9 @@ static int fuse_get_tree(struct fs_context *fsc)
} else {
err = get_tree_nodev(fsc, fuse_fill_super);
}
out_fput:
out:
if (fsc->s_fs_info)
fuse_mount_destroy(fm);
if (ctx->file)
fput(ctx->file);
return err;
@ -1740,10 +1742,8 @@ static void fuse_sb_destroy(struct super_block *sb)
void fuse_mount_destroy(struct fuse_mount *fm)
{
if (fm) {
fuse_conn_put(fm->fc);
kfree(fm);
}
fuse_conn_put(fm->fc);
kfree(fm);
}
EXPORT_SYMBOL(fuse_mount_destroy);