From 2606b28aabd7dea1766c23a105e1124c95409c96 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 20 Sep 2013 17:14:21 +0100 Subject: [PATCH] USB: Fix breakage in ffs_fs_mount() There's a bunch of failure exits in ffs_fs_mount() with seriously broken recovery logics. Most of that appears to stem from misunderstanding of the ->kill_sb() semantics; unlike ->put_super() it is called for *all* superblocks of given type, no matter how (in)complete the setup had been. ->put_super() is called only if ->s_root is not NULL; any failure prior to setting ->s_root will have the call of ->put_super() skipped. ->kill_sb(), OTOH, awaits every superblock that has come from sget(). Current behaviour of ffs_fs_mount(): We have struct ffs_sb_fill_data data on stack there. We do ffs_dev = functionfs_acquire_dev_callback(dev_name); and store that in data.private_data. Then we call mount_nodev(), passing it ffs_sb_fill() as a callback. That will either fail outright, or manage to call ffs_sb_fill(). There we allocate an instance of struct ffs_data, slap the value of ffs_dev (picked from data.private_data) into ffs->private_data and overwrite data.private_data by storing ffs into an overlapping member (data.ffs_data). Then we store ffs into sb->s_fs_info and attempt to set the rest of the things up (root inode, root dentry, then create /ep0 there). Any of those might fail. Should that happen, we get ffs_fs_kill_sb() called before mount_nodev() returns. If mount_nodev() fails for any reason whatsoever, we proceed to functionfs_release_dev_callback(data.ffs_data); That's broken in a lot of ways. Suppose the thing has failed in allocation of e.g. root inode or dentry. We have functionfs_release_dev_callback(ffs); ffs_data_put(ffs); done by ffs_fs_kill_sb() (ffs accessed via sb->s_fs_info), followed by functionfs_release_dev_callback(ffs); from ffs_fs_mount() (via data.ffs_data). Note that the second functionfs_release_dev_callback() has every chance to be done to freed memory. Suppose we fail *before* root inode allocation. What happens then? ffs_fs_kill_sb() doesn't do anything to ffs (it's either not called at all, or it doesn't have a pointer to ffs stored in sb->s_fs_info). And functionfs_release_dev_callback(data.ffs_data); is called by ffs_fs_mount(), but here we are in nasal daemon country - we are reading from a member of union we'd never stored into. In practice, we'll get what we used to store into the overlapping field, i.e. ffs_dev. And then we get screwed, since we treat it (struct gfs_ffs_obj * in disguise, returned by functionfs_acquire_dev_callback()) as struct ffs_data *, pick what would've been ffs_data ->private_data from it (*well* past the actual end of the struct gfs_ffs_obj - struct ffs_data is much bigger) and poke in whatever it points to. FWIW, there's a minor leak on top of all that in case if ffs_sb_fill() fails on kstrdup() - ffs is obviously forgotten. The thing is, there is no point in playing all those games with union. Just allocate and initialize ffs_data *before* calling mount_nodev() and pass a pointer to it via data.ffs_data. And once it's stored in sb->s_fs_info, clear data.ffs_data, so that ffs_fs_mount() knows that it doesn't need to kill the sucker manually - from that point on we'll have it done by ->kill_sb(). Signed-off-by: Al Viro Acked-by: Michal Nazarewicz Cc: stable # 3.3+ Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/f_fs.c | 60 +++++++++++++++++---------------------- 1 file changed, 26 insertions(+), 34 deletions(-) diff --git a/drivers/usb/gadget/f_fs.c b/drivers/usb/gadget/f_fs.c index 1a66c5baa0d1..0658908d8968 100644 --- a/drivers/usb/gadget/f_fs.c +++ b/drivers/usb/gadget/f_fs.c @@ -1034,37 +1034,19 @@ struct ffs_sb_fill_data { struct ffs_file_perms perms; umode_t root_mode; const char *dev_name; - union { - /* set by ffs_fs_mount(), read by ffs_sb_fill() */ - void *private_data; - /* set by ffs_sb_fill(), read by ffs_fs_mount */ - struct ffs_data *ffs_data; - }; + struct ffs_data *ffs_data; }; static int ffs_sb_fill(struct super_block *sb, void *_data, int silent) { struct ffs_sb_fill_data *data = _data; struct inode *inode; - struct ffs_data *ffs; + struct ffs_data *ffs = data->ffs_data; ENTER(); - /* Initialise data */ - ffs = ffs_data_new(); - if (unlikely(!ffs)) - goto Enomem; - ffs->sb = sb; - ffs->dev_name = kstrdup(data->dev_name, GFP_KERNEL); - if (unlikely(!ffs->dev_name)) - goto Enomem; - ffs->file_perms = data->perms; - ffs->private_data = data->private_data; - - /* used by the caller of this function */ - data->ffs_data = ffs; - + data->ffs_data = NULL; sb->s_fs_info = ffs; sb->s_blocksize = PAGE_CACHE_SIZE; sb->s_blocksize_bits = PAGE_CACHE_SHIFT; @@ -1080,17 +1062,14 @@ static int ffs_sb_fill(struct super_block *sb, void *_data, int silent) &data->perms); sb->s_root = d_make_root(inode); if (unlikely(!sb->s_root)) - goto Enomem; + return -ENOMEM; /* EP0 file */ if (unlikely(!ffs_sb_create_file(sb, "ep0", ffs, &ffs_ep0_operations, NULL))) - goto Enomem; + return -ENOMEM; return 0; - -Enomem: - return -ENOMEM; } static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts) @@ -1193,6 +1172,7 @@ ffs_fs_mount(struct file_system_type *t, int flags, struct dentry *rv; int ret; void *ffs_dev; + struct ffs_data *ffs; ENTER(); @@ -1200,18 +1180,30 @@ ffs_fs_mount(struct file_system_type *t, int flags, if (unlikely(ret < 0)) return ERR_PTR(ret); + ffs = ffs_data_new(); + if (unlikely(!ffs)) + return ERR_PTR(-ENOMEM); + ffs->file_perms = data.perms; + + ffs->dev_name = kstrdup(dev_name, GFP_KERNEL); + if (unlikely(!ffs->dev_name)) { + ffs_data_put(ffs); + return ERR_PTR(-ENOMEM); + } + ffs_dev = functionfs_acquire_dev_callback(dev_name); - if (IS_ERR(ffs_dev)) - return ffs_dev; + if (IS_ERR(ffs_dev)) { + ffs_data_put(ffs); + return ERR_CAST(ffs_dev); + } + ffs->private_data = ffs_dev; + data.ffs_data = ffs; - data.dev_name = dev_name; - data.private_data = ffs_dev; rv = mount_nodev(t, flags, &data, ffs_sb_fill); - - /* data.ffs_data is set by ffs_sb_fill */ - if (IS_ERR(rv)) + if (IS_ERR(rv) && data.ffs_data) { functionfs_release_dev_callback(data.ffs_data); - + ffs_data_put(data.ffs_data); + } return rv; } -- GitLab