fs/kernel_file_read: Add "offset" arg for partial reads

To perform partial reads, callers of kernel_read_file*() must have a
non-NULL file_size argument and a preallocated buffer. The new "offset"
argument can then be used to seek to specific locations in the file to
fill the buffer to, at most, "buf_size" per call.

Where possible, the LSM hooks can report whether a full file has been
read or not so that the contents can be reasoned about.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201002173828.2099543-14-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index d9a1801..79f8646 100644 (file)
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -499,7 +499,7 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
                fw_priv->size = 0;
 
                /* load firmware files from the mount namespace of init */
-               rc = kernel_read_file_from_path_initns(path, &buffer, msize,
+               rc = kernel_read_file_from_path_initns(path, 0, &buffer, msize,
                                                       NULL,
                                                       READING_FIRMWARE);
                if (rc < 0) {

diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index d73bc3f..90d255f 100644 (file)
--- a/fs/kernel_read_file.c
+++ b/fs/kernel_read_file.c
@@ -9,6 +9,7 @@
  * kernel_read_file() - read file contents into a kernel buffer
  *
  * @file       file to read from
+ * @offset     where to start reading from (see below).
  * @buf                pointer to a "void *" buffer for reading into (if
  *             *@buf is NULL, a buffer will be allocated, and
  *             @buf_size will be ignored)
@@ -19,19 +20,31 @@
  * @id         the kernel_read_file_id identifying the type of
  *             file contents being read (for LSMs to examine)
  *
+ * @offset must be 0 unless both @buf and @file_size are non-NULL
+ * (i.e. the caller must be expecting to read partial file contents
+ * via an already-allocated @buf, in at most @buf_size chunks, and
+ * will be able to determine when the entire file was read by
+ * checking @file_size). This isn't a recommended way to read a
+ * file, though, since it is possible that the contents might
+ * change between calls to kernel_read_file().
+ *
  * Returns number of bytes read (no single read will be bigger
  * than INT_MAX), or negative on error.
  *
  */
-int kernel_read_file(struct file *file, void **buf,
+int kernel_read_file(struct file *file, loff_t offset, void **buf,
                     size_t buf_size, size_t *file_size,
                     enum kernel_read_file_id id)
 {
        loff_t i_size, pos;
-       ssize_t bytes = 0;
+       size_t copied;
        void *allocated = NULL;
+       bool whole_file;
        int ret;
 
+       if (offset != 0 && (!*buf || !file_size))
+               return -EINVAL;
+
        if (!S_ISREG(file_inode(file)->i_mode))
                return -EINVAL;
 
@@ -39,19 +52,27 @@ int kernel_read_file(struct file *file, void **buf,
        if (ret)
                return ret;
 
-       ret = security_kernel_read_file(file, id, true);
-       if (ret)
-               goto out;
-
        i_size = i_size_read(file_inode(file));
        if (i_size <= 0) {
                ret = -EINVAL;
                goto out;
        }
-       if (i_size > INT_MAX || i_size > buf_size) {
+       /* The file is too big for sane activities. */
+       if (i_size > INT_MAX) {
+               ret = -EFBIG;
+               goto out;
+       }
+       /* The entire file cannot be read in one buffer. */
+       if (!file_size && offset == 0 && i_size > buf_size) {
                ret = -EFBIG;
                goto out;
        }
+
+       whole_file = (offset == 0 && i_size <= buf_size);
+       ret = security_kernel_read_file(file, id, whole_file);
+       if (ret)
+               goto out;
+
        if (file_size)
                *file_size = i_size;
 
@@ -62,9 +83,14 @@ int kernel_read_file(struct file *file, void **buf,
                goto out;
        }
 
-       pos = 0;
-       while (pos < i_size) {
-               bytes = kernel_read(file, *buf + pos, i_size - pos, &pos);
+       pos = offset;
+       copied = 0;
+       while (copied < buf_size) {
+               ssize_t bytes;
+               size_t wanted = min_t(size_t, buf_size - copied,
+                                             i_size - pos);
+
+               bytes = kernel_read(file, *buf + copied, wanted, &pos);
                if (bytes < 0) {
                        ret = bytes;
                        goto out_free;
@@ -72,14 +98,17 @@ int kernel_read_file(struct file *file, void **buf,
 
                if (bytes == 0)
                        break;
+               copied += bytes;
        }
 
-       if (pos != i_size) {
-               ret = -EIO;
-               goto out_free;
-       }
+       if (whole_file) {
+               if (pos != i_size) {
+                       ret = -EIO;
+                       goto out_free;
+               }
 
-       ret = security_kernel_post_read_file(file, *buf, i_size, id);
+               ret = security_kernel_post_read_file(file, *buf, i_size, id);
+       }
 
 out_free:
        if (ret < 0) {
@@ -91,11 +120,11 @@ out_free:
 
 out:
        allow_write_access(file);
-       return ret == 0 ? pos : ret;
+       return ret == 0 ? copied : ret;
 }
 EXPORT_SYMBOL_GPL(kernel_read_file);
 
-int kernel_read_file_from_path(const char *path, void **buf,
+int kernel_read_file_from_path(const char *path, loff_t offset, void **buf,
                               size_t buf_size, size_t *file_size,
                               enum kernel_read_file_id id)
 {
@@ -109,14 +138,15 @@ int kernel_read_file_from_path(const char *path, void **buf,
        if (IS_ERR(file))
                return PTR_ERR(file);
 
-       ret = kernel_read_file(file, buf, buf_size, file_size, id);
+       ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
        fput(file);
        return ret;
 }
 EXPORT_SYMBOL_GPL(kernel_read_file_from_path);
 
-int kernel_read_file_from_path_initns(const char *path, void **buf,
-                                     size_t buf_size, size_t *file_size,
+int kernel_read_file_from_path_initns(const char *path, loff_t offset,
+                                     void **buf, size_t buf_size,
+                                     size_t *file_size,
                                      enum kernel_read_file_id id)
 {
        struct file *file;
@@ -135,14 +165,14 @@ int kernel_read_file_from_path_initns(const char *path, void **buf,
        if (IS_ERR(file))
                return PTR_ERR(file);
 
-       ret = kernel_read_file(file, buf, buf_size, file_size, id);
+       ret = kernel_read_file(file, offset, buf, buf_size, file_size, id);
        fput(file);
        return ret;
 }
 EXPORT_SYMBOL_GPL(kernel_read_file_from_path_initns);
 
-int kernel_read_file_from_fd(int fd, void **buf, size_t buf_size,
-                            size_t *file_size,
+int kernel_read_file_from_fd(int fd, loff_t offset, void **buf,
+                            size_t buf_size, size_t *file_size,
                             enum kernel_read_file_id id)
 {
        struct fd f = fdget(fd);
@@ -151,7 +181,7 @@ int kernel_read_file_from_fd(int fd, void **buf, size_t buf_size,
        if (!f.file)
                goto out;
 
-       ret = kernel_read_file(f.file, buf, buf_size, file_size, id);
+       ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id);
 out:
        fdput(f);
        return ret;

diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
index 023293e..575ffa1 100644 (file)
--- a/include/linux/kernel_read_file.h
+++ b/include/linux/kernel_read_file.h
@@ -35,19 +35,19 @@ static inline const char *kernel_read_file_id_str(enum kernel_read_file_id id)
        return kernel_read_file_str[id];
 }
 
-int kernel_read_file(struct file *file,
+int kernel_read_file(struct file *file, loff_t offset,
                     void **buf, size_t buf_size,
                     size_t *file_size,
                     enum kernel_read_file_id id);
-int kernel_read_file_from_path(const char *path,
+int kernel_read_file_from_path(const char *path, loff_t offset,
                               void **buf, size_t buf_size,
                               size_t *file_size,
                               enum kernel_read_file_id id);
-int kernel_read_file_from_path_initns(const char *path,
+int kernel_read_file_from_path_initns(const char *path, loff_t offset,
                                      void **buf, size_t buf_size,
                                      size_t *file_size,
                                      enum kernel_read_file_id id);
-int kernel_read_file_from_fd(int fd,
+int kernel_read_file_from_fd(int fd, loff_t offset,
                             void **buf, size_t buf_size,
                             size_t *file_size,
                             enum kernel_read_file_id id);

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index ee51c10..84f7316 100644 (file)
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -221,7 +221,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
        int ret;
        void *ldata;
 
-       ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
+       ret = kernel_read_file_from_fd(kernel_fd, 0, &image->kernel_buf,
                                       INT_MAX, NULL, READING_KEXEC_IMAGE);
        if (ret < 0)
                return ret;
@@ -241,7 +241,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
 #endif
        /* It is possible that there no initramfs is being loaded */
        if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
-               ret = kernel_read_file_from_fd(initrd_fd, &image->initrd_buf,
+               ret = kernel_read_file_from_fd(initrd_fd, 0, &image->initrd_buf,
                                               INT_MAX, NULL,
                                               READING_KEXEC_INITRAMFS);
                if (ret < 0)

diff --git a/kernel/module.c b/kernel/module.c
index adfa21d..9c578e4 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4054,7 +4054,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
                      |MODULE_INIT_IGNORE_VERMAGIC))
                return -EINVAL;
 
-       err = kernel_read_file_from_fd(fd, &hdr, INT_MAX, NULL,
+       err = kernel_read_file_from_fd(fd, 0, &hdr, INT_MAX, NULL,
                                       READING_MODULE);
        if (err < 0)
                return err;

diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index 8a523df..0f518dc 100644 (file)
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -175,7 +175,7 @@ int __init integrity_load_x509(const unsigned int id, const char *path)
        int rc;
        key_perm_t perm;
 
-       rc = kernel_read_file_from_path(path, &data, INT_MAX, NULL,
+       rc = kernel_read_file_from_path(path, 0, &data, INT_MAX, NULL,
                                        READING_X509_CERTIFICATE);
        if (rc < 0) {
                pr_err("Unable to open file: %s (%d)", path, rc);

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 5fc56cc..ea8ff8a 100644 (file)
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -284,7 +284,8 @@ static ssize_t ima_read_policy(char *path)
        datap = path;
        strsep(&datap, "\n");
 
-       rc = kernel_read_file_from_path(path, &data, INT_MAX, NULL, READING_POLICY);
+       rc = kernel_read_file_from_path(path, 0, &data, INT_MAX, NULL,
+                                       READING_POLICY);
        if (rc < 0) {
                pr_err("Unable to open file: %s (%d)", path, rc);
                return rc;