Bug 1225027 (CVE-2023-52779)

In the Linux kernel, the following vulnerability has been resolved:

fs: Pass AT_GETATTR_NOSEC flag to getattr interface function

When vfs_getattr_nosec() calls a filesystem's getattr interface function
then the 'nosec' should propagate into this function so that
vfs_getattr_nosec() can again be called from the filesystem's gettattr
rather than vfs_getattr(). The latter would add unnecessary security
checks that the initial vfs_getattr_nosec() call wanted to avoid.
Therefore, introduce the getattr flag GETATTR_NOSEC and allow to pass
with the new getattr_flags parameter to the getattr interface function.
In overlayfs and ecryptfs use this flag to determine which one of the
two functions to call.

In a recent code change introduced to IMA vfs_getattr_nosec() ended up
calling vfs_getattr() in overlayfs, which in turn called
security_inode_getattr() on an exiting process that did not have
current->fs set anymore, which then caused a kernel NULL pointer
dereference. With this change the call to security_inode_getattr() can
be avoided, thus avoiding the NULL pointer dereference.

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2023-52779
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2023/CVE-2023-52779.mbox
https://git.kernel.org/stable/c/3fb0fa08641903304b9d81d52a379ff031dc41d4
https://git.kernel.org/stable/c/8a924db2d7b5eb69ba08b1a0af46e9f1359a9bdf
https://www.cve.org/CVERecord?id=CVE-2023-52779