dma-buf: Move dma_buf_release() from fops to dentry_ops
commit4ab59c3c63
upstream. 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:bb2bb90304
("dma-buf: add DMA_BUF_SET_NAME ioctls") Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com Cc: <stable@vger.kernel.org> [5.3+] Cc: Arnd Bergmann <arnd@arndb.de> Reported-by: Charan Teja Reddy <charante@codeaurora.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> Tested-by: Charan Teja Reddy <charante@codeaurora.org> Link: https://patchwork.freedesktop.org/patch/msgid/20200611114418.19852-1-sumit.semwal@linaro.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -54,37 +54,11 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
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dentry->d_name.name, ret > 0 ? name : "");
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}
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static const struct dentry_operations dma_buf_dentry_ops = {
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.d_dname = dmabuffs_dname,
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};
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static struct vfsmount *dma_buf_mnt;
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static int dma_buf_fs_init_context(struct fs_context *fc)
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{
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struct pseudo_fs_context *ctx;
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ctx = init_pseudo(fc, DMA_BUF_MAGIC);
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if (!ctx)
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return -ENOMEM;
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ctx->dops = &dma_buf_dentry_ops;
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return 0;
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}
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static struct file_system_type dma_buf_fs_type = {
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.name = "dmabuf",
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.init_fs_context = dma_buf_fs_init_context,
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.kill_sb = kill_anon_super,
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};
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static int dma_buf_release(struct inode *inode, struct file *file)
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static void dma_buf_release(struct dentry *dentry)
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{
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struct dma_buf *dmabuf;
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if (!is_dma_buf_file(file))
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return -EINVAL;
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dmabuf = file->private_data;
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dmabuf = dentry->d_fsdata;
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BUG_ON(dmabuf->vmapping_counter);
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@ -110,9 +84,32 @@ static int dma_buf_release(struct inode *inode, struct file *file)
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module_put(dmabuf->owner);
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kfree(dmabuf->name);
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kfree(dmabuf);
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}
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static const struct dentry_operations dma_buf_dentry_ops = {
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.d_dname = dmabuffs_dname,
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.d_release = dma_buf_release,
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};
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static struct vfsmount *dma_buf_mnt;
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static int dma_buf_fs_init_context(struct fs_context *fc)
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{
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struct pseudo_fs_context *ctx;
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ctx = init_pseudo(fc, DMA_BUF_MAGIC);
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if (!ctx)
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return -ENOMEM;
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ctx->dops = &dma_buf_dentry_ops;
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return 0;
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}
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static struct file_system_type dma_buf_fs_type = {
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.name = "dmabuf",
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.init_fs_context = dma_buf_fs_init_context,
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.kill_sb = kill_anon_super,
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};
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static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
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{
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struct dma_buf *dmabuf;
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@ -412,7 +409,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
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}
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static const struct file_operations dma_buf_fops = {
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.release = dma_buf_release,
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.mmap = dma_buf_mmap_internal,
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.llseek = dma_buf_llseek,
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.poll = dma_buf_poll,
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