watchdog: pretimeout: Fix UAF in watchdog_unregister_governor()

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[ Upstream commit 7362ba0f9c ]

When a watchdog governor is unregistered, it updates existing watchdog
devices that were using this governor by falling back to `default_gov`.

If the governor being unregistered is currently set as `default_gov`,
the `default_gov` is never cleared.  This leads to 2 use-after-free
issues:
1. New watchdog devices registered after this point will inherit the
   dangling `default_gov`.
2. Existing watchdog devices using the unregistered governor will have
   their `wdd->gov` reassigned to the dangling `default_gov`.

Fix the UAF by clearing `default_gov` if it matches the governor being
unregistered.

Fixes: da0d12ff2b ("watchdog: pretimeout: add panic pretimeout governor")
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20260707101803.3598173-1-tzungbi@kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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Tzung-Bi Shih 2026-07-07 10:18:03 +00:00 • committed by Greg Kroah-Hartman

parent 5e07f292ab

commit 472ec1e34f

1 changed files with 2 additions and 0 deletions

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drivers/watchdog/watchdog_pretimeout.c

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