CVE-2023-52909
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk47th percentile - higher than 47% of all known CVEs
Summary
In the Linux kernel's nfsd subsystem, a vulnerability exists in handling cached open files in the nfsd4_open codepath. The issue involves a race where a newly-created nfsd_file can have its PENDING bit cleared while nf_file is still NULL, leading to a crash. Additionally, a memory leak can occur when an existing entry has a valid nf_file. The fix introduces a new nfsd_file_acquirei_opened variant that takes an optional file pointer.
Risk Assessment
The vulnerability can cause kernel crashes (oops) or memory leaks, potentially enabling DoS attacks.
Recommendation
Apply the Linux kernel update containing the fix for CVE-2023-52909. Restrict NFS services to trusted clients.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix handling of cached open files in nfsd4_open codepath Commit fb70bf124b05 ("NFSD: Instantiate a struct file when creating a regular NFSv4 file") added the ability to cache an open fd over a compound. There are a couple of problems with the way this currently works: It's racy, as a newly-created nfsd_file can end up with its PENDING bit cleared while the nf is hashed, and the nf_file pointer is still zeroed out. Other tasks can find it in this state and they expect to see a valid nf_file, and can oops if nf_file is NULL. Also, there is no guarantee that we'll end up creating a new nfsd_file if one is already in the hash. If an extant entry is in the hash with a valid nf_file, nfs4_get_vfs_file will clobber its nf_file pointer with the value of op_file and the old nf_file will leak. Fix both issues by making a new nfsd_file_acquirei_opened variant that takes an optional file pointer. If one is present when this is called, we'll take a new reference to it instead of trying to open the file. If the nfsd_file already has a valid nf_file, we'll just ignore the optional file and pass the nfsd_file back as-is. Also rework the tracepoints a bit to allow for an "opened" variant and don't try to avoid counting acquisitions in the case where we already have a cached open file.