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@linaro.org 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 :)
Fixes: bb2bb9030425 ("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
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.