autofs: ignore notification errors from a replaced pipe
Impact
In the Linux kernel, the following vulnerability has been resolved:
Source excerpt · LinuxAffected packages
Affected products
Vendor version evidence. Product records are separate from automatic dependency matching.
Linux · Linux
Other versions: unaffected
| Version / range | Source status |
|---|---|
| 8d7b48e0bc5fa01a818eac713d4cb0763090cd0e to before 1a177064f501ed4b67873a43aae5d5bdb18b3704 | affected |
| 8d7b48e0bc5fa01a818eac713d4cb0763090cd0e to before fb296391f685d82dbb93621a970fb234cea45280 | affected |
| 8d7b48e0bc5fa01a818eac713d4cb0763090cd0e to before 65676cd4203c0e41a94caf54080a7f0a95434bda | affected |
Linux · Linux
Other versions: affected
| Version / range | Source status |
|---|---|
| 2.6.28 | affected |
| 0 to before 2.6.28 | unaffected |
| 6.18.59 through 6.18.* (inclusive) | unaffected |
| 7.2.13 through 7.2.* (inclusive) | unaffected |
| 7.3 through * (inclusive) | unaffected |
Original source description
In the Linux kernel, the following vulnerability has been resolved:
autofs: ignore notification errors from a replaced pipe
autofs_notify_daemon() takes a reference to the current notification pipe under wq_mutex, then drops the mutex before writing the request. The write can block while the daemon enters catatonic mode and installs a replacement pipe.
If the old pipe's reader is then closed, the delayed write returns -EPIPE and the generic error path enters catatonic mode again. That transition acts on the current superblock state, closes the replacement pipe, and releases the new daemon generation's wait queues.
Only enter catatonic mode when the pipe which failed is still the current pipe. Factor the already-locked transition so the identity check and state change are atomic with respect to another replacement.
This was reproduced on v7.3-rc5-337-gff47652a4b66c in a local QEMU guest. An unprivileged UID 65534 lookup filled the old packet pipe before a normal CATATONIC/SETPIPEFD restart. On the unmodified kernel, the new pipe received HUP and both a pending victim lookup and a later lookup failed with ENOENT in two out of two fresh-mount runs.
With this change, the new pipe remained active, received an intact 304-byte request, and both victim lookups completed in two out of two runs. Normal lookup and restart-without-a-blocked-writer controls passed. No KASAN, oops, refcount, or lock diagnostic was observed. A source reproducer and complete local logs are available privately on request.
The demonstrated impact is limited to denial of a shared autofs service during a legitimate daemon restart. No memory corruption, information leak, privilege escalation, or code execution primitive was observed.