Bug 2297497 (CVE-2024-40913)

Summary: CVE-2024-40913 kernel: cachefiles: defer exposing anon_fd until after copy_to_user() succeeds
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: kernel 6.1.95, kernel 6.6.35, kernel 6.9.6, kernel 6.10-rc4 Doc Type: If docs needed, set a value
Doc Text:
A vulnerability was found in the Linux kernel's cachefiles component, regarding the handling of anonymous file descriptors. This issue occurs when an anonymous fd is exposed to userland before confirming the success of the copy_to_user() operation, which can lead to a use-after-free condition.
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Description OSIDB Bzimport 2024-07-12 13:30:53 UTC 
In the Linux kernel, the following vulnerability has been resolved:

cachefiles: defer exposing anon_fd until after copy_to_user() succeeds

After installing the anonymous fd, we can now see it in userland and close
it. However, at this point we may not have gotten the reference count of
the cache, but we will put it during colse fd, so this may cause a cache
UAF.

So grab the cache reference count before fd_install(). In addition, by
kernel convention, fd is taken over by the user land after fd_install(),
and the kernel should not call close_fd() after that, i.e., it should call
fd_install() after everything is ready, thus fd_install() is called after
copy_to_user() succeeds.
Comment 5 errata-xmlrpc 2024-11-12 09:36:04 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2024:9315 https://access.redhat.com/errata/RHSA-2024:9315