[PATCH 1/2] security: Handle dentries without inode in security_path_post_mknod()

[Mimi Zohar]

On Fri, 2024-03-29 at 11:56 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu at huawei.com>
> 
> Commit 08abce60d63fi ("security: Introduce path_post_mknod hook")
> introduced security_path_post_mknod(), to replace the IMA-specific call to
> ima_post_path_mknod().
> 
> For symmetry with security_path_mknod(), security_path_post_mknod() is
> called after a successful mknod operation, for any file type, rather than
> only for regular files at the time there was the IMA call.
> 
> However, as reported by VFS maintainers, successful mknod operation does
> not mean that the dentry always has an inode attached to it (for example,
> not for FIFOs on a SAMBA mount).
> 
> If that condition happens, the kernel crashes when
> security_path_post_mknod() attempts to verify if the inode associated to
> the dentry is private.
> 
> Add an extra check to first verify if there is an inode attached to the
> dentry, before checking if the inode is private. Also add the same check to
> the current users of the path_post_mknod hook, ima_post_path_mknod() and
> evm_post_path_mknod().
> 
> Finally, use the proper helper, d_backing_inode(), to retrieve the inode
> from the dentry in ima_post_path_mknod().
> 
> Cc: stable at vger.kernel.org # 6.8.x

Huh?  It doesn't need to be backported.

> Reported-by: Steve French <smfrench at gmail.com>
> Closes: 
> https://lore.kernel.org/linux-kernel/CAH2r5msAVzxCUHHG8VKrMPUKQHmBpE6K9_vjhgDa1uAvwx4ppw@mail.gmail.com/
> Fixes: 08abce60d63fi ("security: Introduce path_post_mknod hook")

-> 08abce60d63f

> Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>

Acked-by: Mimi Zohar <zohar at linux.ibm.com>