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Tue, 15 Sep 2026 13:25:45 -0700 (PDT) Received: from nixos.tail966018.ts.net ([2405:9800:b530:f677:2b6:42de:4884:aa25]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33bf5aa1194sm1560592eec.14.2026.09.15.13.25.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 13:25:44 -0700 (PDT) From: Tanawat Jukmongkol To: axboe@kernel.dk, tz2294@columbia.edu Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-next@vger.kernel.org, regressions@lists.linux.dev, Tanawat Jukmongkol Subject: [PATCH] fs/buffer: fix NULL deref on folio-less bh in __bh_submit Date: Wed, 16 Sep 2026 03:25:34 +0700 Message-ID: <20260915202534.468958-1-tanawat.jukmon@gmail.com> X-Mailer: git-send-email 2.47.2 Precedence: bulk X-Mailing-List: linux-next@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit jbd2 submits buffer_heads it allocates directly for journal descriptor and commit-record blocks, which have no folio backing at all - as the comment on buffer_set_crypto_ctx() just above already notes. Unlike that check, and unlike the bh->b_folio check further down in the same function, __bh_submit() calls folio_test_dropbehind(bh->b_folio) unconditionally, so committing a transaction on one of these bh's null-derefs while reading the folio's flags: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: __bh_submit+0x90/0x140 Call Trace: jbd2_journal_commit_transaction kjournald2 kthread Guard the call the same way. Fixes: a2c924c240e7 ("buffer: set BIO_COMPLETE_IN_TASK for dropbehind writeback") Signed-off-by: Tanawat Jukmongkol --- fs/buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/buffer.c b/fs/buffer.c index 427d8a817..4aea0bb08 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1106,7 +1106,7 @@ static void __bh_submit(struct buffer_head *bh, blk_opf_t opf, bio = bio_alloc(bh->b_bdev, 1, opf, GFP_NOIO); - if (folio_test_dropbehind(bh->b_folio) && op_is_write(opf)) + if (bh->b_folio && folio_test_dropbehind(bh->b_folio) && op_is_write(opf)) bio_set_flag(bio, BIO_COMPLETE_IN_TASK); if (IS_ENABLED(CONFIG_FS_ENCRYPTION))