Bug 2395806 (CVE-2025-39819)

Summary: CVE-2025-39819 kernel: fs/smb: Fix inconsistent refcnt update
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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OS: Linux   
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Description OSIDB Bzimport 2025-09-16 14:03:49 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fs/smb: Fix inconsistent refcnt update

A possible inconsistent update of refcount was identified in `smb2_compound_op`.
Such inconsistent update could lead to possible resource leaks.

Why it is a possible bug:
1. In the comment section of the function, it clearly states that the
reference to `cfile` should be dropped after calling this function.
2. Every control flow path would check and drop the reference to
`cfile`, except the patched one.
3. Existing callers would not handle refcount update of `cfile` if
-ENOMEM is returned.

To fix the bug, an extra goto label "out" is added, to make sure that the
cleanup logic would always be respected. As the problem is caused by the
allocation failure of `vars`, the cleanup logic between label "finished"
and "out" can be safely ignored. According to the definition of function
`is_replayable_error`, the error code of "-ENOMEM" is not recoverable.
Therefore, the replay logic also gets ignored.
Comment 1 Keith Grant 2025-09-16 16:11:19 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025091615-CVE-2025-39819-d3c9@gregkh/T