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Sun, 25 Oct 2026 10:11:51 -0700 (PDT) Received: from localhost.localdomain ([98.148.34.5]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-369e8c576ebsm17670582eec.3.2026.10.25.10.11.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Oct 2026 10:11:46 -0700 (PDT) From: Hungyu Lin To: viro@zeniv.linux.org.uk, brauner@kernel.org Cc: jack@suse.cz, akpm@linux-foundation.org, dave.hansen@linux.intel.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Hungyu Lin Subject: [PATCH] libfs: do not extend i_size when no data was copied Date: Sun, 25 Oct 2026 17:11:30 +0000 Message-ID: <20261025171130.16115-1-dennylin0707@gmail.com> X-Mailer: git-send-email 2.43.0 X-Mailing-List: linux-kernel@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 simple_write_end() updates i_size to pos + copied even when copied is zero. A failed buffered write past EOF can therefore extend a ramfs file without writing any data. Since prefaulting was moved to the slow write path, this is reproducible with a one-byte pwrite() at offset 4096 into an empty ramfs file using an unreadable source buffer. The call fails with EFAULT but leaves the file size at 4096. generic_perform_write() calls ->write_end() with copied == 0 before trying to fault in the source buffer. Only extend i_size when data was copied. Keep the existing folio handling so that zero-progress retries and successful writes retain their current behavior. Fixes: 665575cff098 ("filemap: move prefaulting out of hot write path") Cc: stable@vger.kernel.org Signed-off-by: Hungyu Lin --- fs/libfs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/libfs.c b/fs/libfs.c index 8e2cc627bc7f..d889a4a14f41 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -1007,7 +1007,7 @@ static int simple_write_end(const struct kiocb *iocb, * No need to use i_size_read() here, the i_size * cannot change under us because we hold the i_rwsem. */ - if (last_pos > inode->i_size) + if (copied && last_pos > inode->i_size) i_size_write(inode, last_pos); folio_mark_dirty(folio); -- 2.43.0