Hello, If there are no objections to this, I will plan to merge it soon. Daniel, Chris, Chenbo? On Thu, 11 Jun 2020 at 17:14, Sumit Semwal <sumit.semwal@xxxxxxxxxx> wrote: > > Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which > happens if the dma_buf_release() is called while the userspace is > accessing the dma_buf pseudo fs's dmabuffs_dname() in another process, > and dma_buf_release() releases the dmabuf object when the last reference > to the struct file goes away. > > I discussed with Arnd Bergmann, and he suggested that rather than tying > the dma_buf_release() to the file_operations' release(), we can tie it to > the dentry_operations' d_release(), which will be called when the last ref > to the dentry is removed. > > The path exercised by __fput() calls f_op->release() first, and then calls > dput, which eventually calls d_op->d_release(). > > In the 'normal' case, when no userspace access is happening via dma_buf > pseudo fs, there should be exactly one fd, file, dentry and inode, so > closing the fd will kill of everything right away. > > In the presented case, the dentry's d_release() will be called only when > the dentry's last ref is released. > > Therefore, lets move dma_buf_release() from fops->release() to > d_ops->d_release() > > Many thanks to Arnd for his FS insights :) > > [1]: https://lore.kernel.org/patchwork/patch/1238278/ > > Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls") > Reported-by: syzbot+3643a18836bce555bff6@xxxxxxxxxxxxxxxxxxxxxxxxx > Cc: <stable@xxxxxxxxxxxxxxx> [5.3+] > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Reported-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx> > Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx> > Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx> > > --- > v2: per Arnd: Moved dma_buf_release() above to avoid forward declaration; > removed dentry_ops check. > --- > drivers/dma-buf/dma-buf.c | 54 ++++++++++++++++++--------------------- > 1 file changed, 25 insertions(+), 29 deletions(-) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 01ce125f8e8d..412629601ad3 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -54,37 +54,11 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen) > dentry->d_name.name, ret > 0 ? name : ""); > } > > -static const struct dentry_operations dma_buf_dentry_ops = { > - .d_dname = dmabuffs_dname, > -}; > - > -static struct vfsmount *dma_buf_mnt; > - > -static int dma_buf_fs_init_context(struct fs_context *fc) > -{ > - struct pseudo_fs_context *ctx; > - > - ctx = init_pseudo(fc, DMA_BUF_MAGIC); > - if (!ctx) > - return -ENOMEM; > - ctx->dops = &dma_buf_dentry_ops; > - return 0; > -} > - > -static struct file_system_type dma_buf_fs_type = { > - .name = "dmabuf", > - .init_fs_context = dma_buf_fs_init_context, > - .kill_sb = kill_anon_super, > -}; > - > -static int dma_buf_release(struct inode *inode, struct file *file) > +static void dma_buf_release(struct dentry *dentry) > { > struct dma_buf *dmabuf; > > - if (!is_dma_buf_file(file)) > - return -EINVAL; > - > - dmabuf = file->private_data; > + dmabuf = dentry->d_fsdata; > > BUG_ON(dmabuf->vmapping_counter); > > @@ -110,9 +84,32 @@ static int dma_buf_release(struct inode *inode, struct file *file) > module_put(dmabuf->owner); > kfree(dmabuf->name); > kfree(dmabuf); > +} > + > +static const struct dentry_operations dma_buf_dentry_ops = { > + .d_dname = dmabuffs_dname, > + .d_release = dma_buf_release, > +}; > + > +static struct vfsmount *dma_buf_mnt; > + > +static int dma_buf_fs_init_context(struct fs_context *fc) > +{ > + struct pseudo_fs_context *ctx; > + > + ctx = init_pseudo(fc, DMA_BUF_MAGIC); > + if (!ctx) > + return -ENOMEM; > + ctx->dops = &dma_buf_dentry_ops; > return 0; > } > > +static struct file_system_type dma_buf_fs_type = { > + .name = "dmabuf", > + .init_fs_context = dma_buf_fs_init_context, > + .kill_sb = kill_anon_super, > +}; > + > static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma) > { > struct dma_buf *dmabuf; > @@ -412,7 +409,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) > } > > static const struct file_operations dma_buf_fops = { > - .release = dma_buf_release, > .mmap = dma_buf_mmap_internal, > .llseek = dma_buf_llseek, > .poll = dma_buf_poll, > -- > 2.27.0 > Best, Sumit.
