Unverified Commit b68f91ef authored by Deepakkumar Karn's avatar Deepakkumar Karn Committed by Christian Brauner
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fs/buffer: add alert in try_to_free_buffers() for folios without buffers 



try_to_free_buffers() can be called on folios with no buffers attached
when filemap_release_folio() is invoked on a folio belonging to a mapping
with AS_RELEASE_ALWAYS set but no release_folio operation defined.

In such cases, folio_needs_release() returns true because of the
AS_RELEASE_ALWAYS flag, but the folio has no private buffer data. This
causes try_to_free_buffers() to call drop_buffers() on a folio with no
buffers, leading to a null pointer dereference.

Adding a check in try_to_free_buffers() to return early if the folio has no
buffers attached, with WARN_ON_ONCE() to alert about the misconfiguration.
This provides defensive hardening.

Signed-off-by: default avatarDeepakkumar Karn <dkarn@redhat.com>
Link: https://patch.msgid.link/20251211131211.308021-1-dkarn@redhat.com


Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 961b2ad1

fs/buffer.c

+4 −0
Original line number Diff line number Diff line
@@ -2948,6 +2948,10 @@ bool try_to_free_buffers(struct folio *folio) 
	if (folio_test_writeback(folio))

		return false;



	/* Misconfigured folio check */

	if (WARN_ON_ONCE(!folio_buffers(folio)))

		return true;



	if (mapping == NULL) {		/* can this still happen? */

		ret = drop_buffers(folio, &buffers_to_free);

		goto out;