From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794406171; b=N4GoC7BskjXAsqOmKZ4NFaaZ7EIuS3kXkOGEYx0ar1GGQ1v9E5AKLgh5q2KwWQoULeC8 37IjXPmDXCctyGc73VWBGa/vgIWm6iLsEqwose+szNNY31Fk0HaGRQG4K9Vco9LKfz2pI kdX+UGnMhf8JrHOZp4DPOeenOMlM6iF3dPumq3MPT5HRJQTRM0v2Bxlbt6moVVAl18l0I hajXfRrX9rIgPvg1E7jnOvrdEoVdFK3R27cZU8Iiu8SeK0/OE4J/TMdqihLPUtvl3B1TX jnMiBpgZTrOVEXSSX9nIQZDccavpzPHkYJCGsEQkoDyGotqaH72LaQFj011/nzwMcHA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794406171; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=KdKUCnPFJ0XNieEZMtFgCzJnD6svpgJqqUzsv53u0js=; b=jT6j86VGNPtft+taOb8dAcBrLkq4WxliWKNbiy+UuxCqJ1Kse8D2Dn5zkPSEmEGIw2I7 gjbLRuRehstKoHzSqBfxU9Ub1cyUqaiH3ND18rLYMiHQsRFcJoU7GUCG+mbxegYX+4MPN I8Pc3er3FbDdxSbWgsCrklWCOXIjN7lqyuHxGcUTDnYzTZw7MMoDXNvAz2IT1JxiK4ojJ OQCLQPr5KIHB5uCp275cMIjAo4aVAv56ew+NT1v7qJ2xizzyX11FD2Gav16Kms/5zGF0I NXIDtc0Unwed06f/E+ABM0SqtBpQoxKl8Yv3qbjXaP00OXDxiE29iCH9+ssJXUW/XIw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=jHADfbH2; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 039B9606A321 for ; Wed, 11 Nov 2026 14:09:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=jHADfbH2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id F255D1F00A05; Wed, 11 Nov 2026 14:09:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794406170; bh=KdKUCnPFJ0XNieEZMtFgCzJnD6svpgJqqUzsv53u0js=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=jHADfbH2Kn1g0rq9KyvrDBKLLHGEgU76oG77FYilQwcsGYQmpbWRFlA1VDsmEcJ3P uqR4ByZ9AXg3bjXToFUOx+c48Ugaau9ywjY1mGqv6qVVC1R2aYn/k1BCXBYJuhmVmK 5j8dhBoa0DXULfOtUnOOTUwFB3tLBFqPXQ4UrmRq31kHLHS7ckXHGcm2fztdtBTUjb aO9mhSJX7BiV4xQo9tSPQya61YgVyhlNxl4wgLchTrm5igPE3jFGDqr2A3YIlTkfCn yaqYsZL9uXD/pKhXsepN5E+TCjYvOYjCT26l6a4hWil03zN3R0Z+T/nRrgIz2LKrk/ pwwY6jK4YPUjQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Josef Bacik , Sasha Levin Subject: [PATCH 6.18.y] iomap: don't mark unwritten parts of a folio uptodate Date: Wed, 11 Nov 2026 09:09:28 -0500 Message-ID: <20261111140848.2185493-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107051550-failed-6.18-a4193b4af359@kernel.org> References: <20261107051550-failed-6.18-a4193b4af359@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit a4193b4af359db84b2cdf3a040752861984c636b ] For a buffered write into a hole, an unwritten or new extent, or past EOF __iomap_write_begin() zeroes the parts of the blocks outside of the write and then marks the blocks uptodate. That includes the range of the write itself which still holds whatever was in the folio before. It only becomes valid once the copy from userspace has filled it in. But the copy can come up short and __iomap_write_end() only rejects a short copy if the folio isn't uptodate. If the zeroed blocks were all that was missing the folio is uptodate by then, the short copy is accepted, and the rest of the range is exposed to readers and can end up on disk. A source buffer that ends in an unmapped page is enough: ftruncate(fd, 4096); pwrite(fd, p, 3000, 100); /* 16 bytes at p, then PROT_NONE */ pread(fd, buf, 4096, 0); The write returns 16 and the read returns 2984 bytes of whatever was in that page before. If other blocks of the folio aren't uptodate the short copy is rejected but the zeroed blocks keep their uptodate bits and the retry with the copied length leaves the same bytes behind. Only mark blocks uptodate in __iomap_write_begin() after reading them. __iomap_write_end() marks the zeroed blocks uptodate once the copy has succeeded and rejects a short copy. Willy reported this back in 2024 (cf. [1]) and Zhang Yi posted the same fix (cf. [2]) but it never got merged. [1]: https://lore.kernel.org/all/ZqsN5ouQTEc1KAzV@casper.infradead.org [2]: https://lore.kernel.org/all/20240812121159.3775074-6-yi.zhang@huaweicloud.com Fixes: 9dc55f1389f9 ("iomap: add support for sub-pagesize buffered I/O without buffer heads") Reported-by: Josef Bacik Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20261029-work-iomap-ai-fixes-v1-1-7eda63bc1b13@kernel.org Signed-off-by: Christian Brauner (Amutable) [ sashal: placed iomap_set_range_uptodate() after the read-error check because IOMAP_F_ZERO_TAIL handling is absent ] Signed-off-by: Sasha Levin --- fs/iomap/buffered-io.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index c9ece378687b9..cbd729ef50ab7 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -766,6 +766,7 @@ static int __iomap_write_begin(const struct iomap_iter *iter, if (iomap_block_needs_zeroing(iter, block_start)) { if (WARN_ON_ONCE(iter->flags & IOMAP_UNSHARE)) return -EIO; + /* uptodate once copied, see __iomap_write_end() */ folio_zero_segments(folio, poff, from, to, poff + plen); } else { int status; @@ -781,8 +782,8 @@ static int __iomap_write_begin(const struct iomap_iter *iter, folio, block_start, plen); if (status) return status; + iomap_set_range_uptodate(folio, poff, plen); } - iomap_set_range_uptodate(folio, poff, plen); } while ((block_start += plen) < block_end); return 0; -- 2.53.0