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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id k5sm14254077pfg.215.2021.03.15.10.48.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Mar 2021 10:48:58 -0700 (PDT) From: Kees Cook To: Andrew Morton Cc: Kees Cook , Greg Kroah-Hartman , Michal Hocko , Alexey Dobriyan , Lee Duncan , Chris Leech , Adam Nichols , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer Date: Mon, 15 Mar 2021 10:48:51 -0700 Message-Id: <20210315174851.622228-1-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Patch-Hashes: v=1; h=sha256; g=8127f4bb12fc6c17d3829b992d9a4a2e95e55109; i=wnTs9CQ9b8oyAQUYWk1TWb6rr60OLTnvw/rrLAiBrmk=; m=WalZI6OWPnXJm31CATxJMvj5D+0cNcW5LRPeotCFpyY=; p=zv6zDQp+zJmS7mw61IUyZUpJiDoSaUWpqGFE94Dk8kY= X-Patch-Sig: m=pgp; i=keescook@chromium.org; s=0x0x8972F4DFDC6DC026; b=iQIzBAABCgAdFiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAmBPngIACgkQiXL039xtwCYaRA//bG9 CB3WWFg4jlT5EKm/W144wZYrWglGNAxyEPNd5poScEppgxVgn/GH0OVQqpJJ0L4YFWnJRdYVA390F yfuOuok9B61Vb9/pZ8M17bLNDu0bFnqkPm6he8p3lQWS1k5OwwT+a2O8TjTOLHG0XurastgeTAXF7 l77h6KV2VoX7QtaZRhAGSROGDU+z2Hzm1eX9bGnFM/o5K4GXO8V+pjkwqt+6fEc0GyydBoVYZuMDn AW2pqOlg1AtuvxPVTda7oKblHRPtrRE3FCZjXLvDCzBrsJEHKi+RgcRO1fvmVcSaa3GTDZJndNHuY Pa5tI1DrhWUnBvzWUKTfyWhsneDYLIfFoJ0D+x55pzM0DSGkoO5/SSnGNX6Lau0x+c+k8d0gM0Abi 9pgQxbhcIiW04KZvLrvl4B1EjgZRuXaPWq7nVR6GHjgUGO/SFbEnf8lR3PtbzZMxWKXYyohBuCnHm flNEXnYN+9zcrASK6lQ/KH5pjfJ+YQQlXvI5uuXxesWztdEbCkgOOcqcjs0XSXMZnnAXaU3cuBjhD pTz9vVXDOtiT7ZOiTjLmfVwsUEkCvx0KnBd9u+3tz3zjqft4qWDsQykY/bieSNeupTViLaKuLp0VR JwGDU0TZl5vcvYOo0O1HI9cZtOjet792j0GQ1qDpEH5oEEs7pwEpwCMEc1ZmjwbY= Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org The sysfs interface to seq_file continues to be rather fragile, as seen with some recent exploits[1]. Move the seq_file buffer to the vmap area (while retaining the accounting flag), since it has guard pages that will catch and stop linear overflows. This seems justified given that seq_file already uses kvmalloc(), is almost always using a PAGE_SIZE or larger allocation, has allocations are normally short lived, and is not normally on a performance critical path. [1] https://blog.grimm-co.com/2021/03/new-old-bugs-in-linux-kernel.html Signed-off-by: Kees Cook --- fs/seq_file.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/fs/seq_file.c b/fs/seq_file.c index cb11a34fb871..16fb4a4e61e3 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -32,7 +32,12 @@ static void seq_set_overflow(struct seq_file *m) static void *seq_buf_alloc(unsigned long size) { - return kvmalloc(size, GFP_KERNEL_ACCOUNT); + /* + * To be proactively defensive against buggy seq_get_buf() callers + * (i.e. sysfs handlers), use the vmap area to gain the trailing + * guard page which will protect against linear buffer overflows. + */ + return __vmalloc(size, GFP_KERNEL_ACCOUNT); } /** @@ -130,7 +135,7 @@ static int traverse(struct seq_file *m, loff_t offset) Eoverflow: m->op->stop(m, p); - kvfree(m->buf); + vfree(m->buf); m->count = 0; m->buf = seq_buf_alloc(m->size <<= 1); return !m->buf ? -ENOMEM : -EAGAIN; @@ -237,7 +242,7 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter) goto Fill; // need a bigger buffer m->op->stop(m, p); - kvfree(m->buf); + vfree(m->buf); m->count = 0; m->buf = seq_buf_alloc(m->size <<= 1); if (!m->buf) @@ -349,7 +354,7 @@ EXPORT_SYMBOL(seq_lseek); int seq_release(struct inode *inode, struct file *file) { struct seq_file *m = file->private_data; - kvfree(m->buf); + vfree(m->buf); kmem_cache_free(seq_file_cache, m); return 0; } @@ -585,7 +590,7 @@ int single_open_size(struct file *file, int (*show)(struct seq_file *, void *), return -ENOMEM; ret = single_open(file, show, data); if (ret) { - kvfree(buf); + vfree(buf); return ret; } ((struct seq_file *)file->private_data)->buf = buf; -- 2.25.1