Bug 2425102 (CVE-2023-54099)

Summary: CVE-2023-54099 kernel: fs: Protect reconfiguration of sb read-write from racing writes
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: low    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A race condition was found in the Linux kernel's filesystem remount code. When remounting a filesystem from read-only to read-write, the SB_RDONLY flag is cleared before the filesystem is fully prepared to accept writes. This allows userspace writes to race with filesystem initialization operations like quota file preparation, potentially causing filesystem corruption or crashes.
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Description OSIDB Bzimport 2025-12-24 14:02:58 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fs: Protect reconfiguration of sb read-write from racing writes

The reconfigure / remount code takes a lot of effort to protect
filesystem's reconfiguration code from racing writes on remounting
read-only. However during remounting read-only filesystem to read-write
mode userspace writes can start immediately once we clear SB_RDONLY
flag. This is inconvenient for example for ext4 because we need to do
some writes to the filesystem (such as preparation of quota files)
before we can take userspace writes so we are clearing SB_RDONLY flag
before we are fully ready to accept userpace writes and syzbot has found
a way to exploit this [1]. Also as far as I'm reading the code
the filesystem remount code was protected from racing writes in the
legacy mount path by the mount's MNT_READONLY flag so this is relatively
new problem. It is actually fairly easy to protect remount read-write
from racing writes using sb->s_readonly_remount flag so let's just do
that instead of having to workaround these races in the filesystem code.

[1] https://lore.kernel.org/all/00000000000006a0df05f6667499@google.com/T/
Comment 1 Alexander B 2025-12-25 02:29:51 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025122409-CVE-2023-54099-4143@gregkh/T