Commit 4ab59c3c authored by Sumit Semwal's avatar Sumit Semwal

dma-buf: Move dma_buf_release() from fops to dentry_ops

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: bb2bb903 ("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: default avatarCharan Teja Reddy <charante@codeaurora.org>
Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarSumit Semwal <sumit.semwal@linaro.org>
Tested-by: default avatarCharan Teja Reddy <charante@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200611114418.19852-1-sumit.semwal@linaro.org
parent dc5bdb68
...@@ -54,37 +54,11 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen) ...@@ -54,37 +54,11 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
dentry->d_name.name, ret > 0 ? name : ""); dentry->d_name.name, ret > 0 ? name : "");
} }
static const struct dentry_operations dma_buf_dentry_ops = { static void dma_buf_release(struct dentry *dentry)
.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)
{ {
struct dma_buf *dmabuf; struct dma_buf *dmabuf;
if (!is_dma_buf_file(file)) dmabuf = dentry->d_fsdata;
return -EINVAL;
dmabuf = file->private_data;
BUG_ON(dmabuf->vmapping_counter); BUG_ON(dmabuf->vmapping_counter);
...@@ -110,9 +84,32 @@ static int dma_buf_release(struct inode *inode, struct file *file) ...@@ -110,9 +84,32 @@ static int dma_buf_release(struct inode *inode, struct file *file)
module_put(dmabuf->owner); module_put(dmabuf->owner);
kfree(dmabuf->name); kfree(dmabuf->name);
kfree(dmabuf); 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; 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) static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
{ {
struct dma_buf *dmabuf; struct dma_buf *dmabuf;
...@@ -412,7 +409,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) ...@@ -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 = { static const struct file_operations dma_buf_fops = {
.release = dma_buf_release,
.mmap = dma_buf_mmap_internal, .mmap = dma_buf_mmap_internal,
.llseek = dma_buf_llseek, .llseek = dma_buf_llseek,
.poll = dma_buf_poll, .poll = dma_buf_poll,
......
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