Hi Kees,

On 2020-07-17 10:43 a.m., Kees Cook wrote:
In preparation for refactoring kernel_read_file*(), remove the redundant
"size" argument which is not needed: it can be included in the return
I don't think the size argument is redundant though.
The existing kernel_read_file functions always read the whole file.
Now, what happens if the file is bigger than the buffer.
How does kernel_read_file know it read the whole file by looking at the return value?
code, with callers adjusted. (VFS reads already cannot be larger than
INT_MAX.)

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
  drivers/base/firmware_loader/main.c |  8 ++++----
  fs/kernel_read_file.c               | 20 +++++++++-----------
  include/linux/kernel_read_file.h    |  8 ++++----
  kernel/kexec_file.c                 | 13 ++++++-------
  kernel/module.c                     |  7 +++----
  security/integrity/digsig.c         |  5 +++--
  security/integrity/ima/ima_fs.c     |  5 +++--
  7 files changed, 32 insertions(+), 34 deletions(-)

diff --git a/drivers/base/firmware_loader/main.c 
b/drivers/base/firmware_loader/main.c
index d4a413ea48ce..ea419c7d3d34 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -462,7 +462,7 @@ fw_get_filesystem_firmware(struct device *device, struct 
fw_priv *fw_priv,
                                             size_t in_size,
                                             const void *in_buffer))
  {
-       loff_t size;
+       size_t size;
        int i, len;
        int rc = -ENOENT;
        char *path;
@@ -494,10 +494,9 @@ 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,
-                                                      &size, msize,
+               rc = kernel_read_file_from_path_initns(path, &buffer, msize,
                                                       READING_FIRMWARE);
-               if (rc) {
+               if (rc < 0) {
                        if (rc != -ENOENT)
                                dev_warn(device, "loading %s failed with error 
%d\n",
                                         path, rc);
@@ -506,6 +505,7 @@ fw_get_filesystem_firmware(struct device *device, struct 
fw_priv *fw_priv,
                                         path);
                        continue;
                }
+               size = rc;
                dev_dbg(device, "Loading firmware from %s\n", path);
                if (decompress) {
                        dev_dbg(device, "f/w decompressing %s\n",
diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index 54d972d4befc..dc28a8def597 100644
--- a/fs/kernel_read_file.c
+++ b/fs/kernel_read_file.c
@@ -5,7 +5,7 @@
  #include <linux/security.h>
  #include <linux/vmalloc.h>
-int kernel_read_file(struct file *file, void **buf, loff_t *size,
+int kernel_read_file(struct file *file, void **buf,
                     loff_t max_size, enum kernel_read_file_id id)
  {
        loff_t i_size, pos;
@@ -29,7 +29,7 @@ int kernel_read_file(struct file *file, void **buf, loff_t 
*size,
                ret = -EINVAL;
                goto out;
        }
-       if (i_size > SIZE_MAX || (max_size > 0 && i_size > max_size)) {
+       if (i_size > INT_MAX || (max_size > 0 && i_size > max_size)) {
Should this be SSIZE_MAX?
                ret = -EFBIG;
                goto out;
        }
@@ -59,8 +59,6 @@ int kernel_read_file(struct file *file, void **buf, loff_t 
*size,
        }
ret = security_kernel_post_read_file(file, *buf, i_size, id);
-       if (!ret)
-               *size = pos;
out_free:
        if (ret < 0) {
@@ -72,11 +70,11 @@ int kernel_read_file(struct file *file, void **buf, loff_t 
*size,
out:
        allow_write_access(file);
-       return ret;
+       return ret == 0 ? pos : ret;
  }
  EXPORT_SYMBOL_GPL(kernel_read_file);
-int kernel_read_file_from_path(const char *path, void **buf, loff_t *size,
+int kernel_read_file_from_path(const char *path, void **buf,
                               loff_t max_size, enum kernel_read_file_id id)
  {
        struct file *file;
@@ -89,14 +87,14 @@ int kernel_read_file_from_path(const char *path, void 
**buf, loff_t *size,
        if (IS_ERR(file))
                return PTR_ERR(file);
- ret = kernel_read_file(file, buf, size, max_size, id);
+       ret = kernel_read_file(file, buf, max_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,
-                                     loff_t *size, loff_t max_size,
+                                     loff_t max_size,
                                      enum kernel_read_file_id id)
  {
        struct file *file;
@@ -115,13 +113,13 @@ 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, size, max_size, id);
+       ret = kernel_read_file(file, buf, max_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, loff_t *size, loff_t max_size,
+int kernel_read_file_from_fd(int fd, void **buf, loff_t max_size,
                             enum kernel_read_file_id id)
  {
        struct fd f = fdget(fd);
@@ -130,7 +128,7 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t 
*size, loff_t max_size,
        if (!f.file)
                goto out;
- ret = kernel_read_file(f.file, buf, size, max_size, id);
+       ret = kernel_read_file(f.file, buf, max_size, id);
  out:
        fdput(f);
        return ret;
diff --git a/include/linux/kernel_read_file.h b/include/linux/kernel_read_file.h
index 78cf3d7dc835..0ca0bdbed1bd 100644
--- a/include/linux/kernel_read_file.h
+++ b/include/linux/kernel_read_file.h
@@ -36,16 +36,16 @@ static inline const char *kernel_read_file_id_str(enum 
kernel_read_file_id id)
  }
int kernel_read_file(struct file *file,
-                    void **buf, loff_t *size, loff_t max_size,
+                    void **buf, loff_t max_size,
                     enum kernel_read_file_id id);
  int kernel_read_file_from_path(const char *path,
-                              void **buf, loff_t *size, loff_t max_size,
+                              void **buf, loff_t max_size,
                               enum kernel_read_file_id id);
  int kernel_read_file_from_path_initns(const char *path,
-                                     void **buf, loff_t *size, loff_t max_size,
+                                     void **buf, loff_t max_size,
                                      enum kernel_read_file_id id);
  int kernel_read_file_from_fd(int fd,
-                            void **buf, loff_t *size, loff_t max_size,
+                            void **buf, loff_t max_size,
                             enum kernel_read_file_id id);
#endif /* _LINUX_KERNEL_READ_FILE_H */
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 1358069ce9e9..a201bbb19158 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -220,13 +220,12 @@ kimage_file_prepare_segments(struct kimage *image, int 
kernel_fd, int initrd_fd,
  {
        int ret;
        void *ldata;
-       loff_t size;
ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
-                                      &size, INT_MAX, READING_KEXEC_IMAGE);
-       if (ret)
+                                      INT_MAX, READING_KEXEC_IMAGE);
+       if (ret < 0)
                return ret;
-       image->kernel_buf_len = size;
+       image->kernel_buf_len = ret;
/* Call arch image probe handlers */
        ret = arch_kexec_kernel_image_probe(image, image->kernel_buf,
@@ -243,11 +242,11 @@ kimage_file_prepare_segments(struct kimage *image, int 
kernel_fd, int initrd_fd,
        /* 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,
-                                              &size, INT_MAX,
+                                              INT_MAX,
                                               READING_KEXEC_INITRAMFS);
-               if (ret)
+               if (ret < 0)
                        goto out;
-               image->initrd_buf_len = size;
+               image->initrd_buf_len = ret;
        }
if (cmdline_len) {
diff --git a/kernel/module.c b/kernel/module.c
index e9765803601b..b6fd4f51cc30 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3988,7 +3988,6 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
  SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
  {
        struct load_info info = { };
-       loff_t size;
        void *hdr = NULL;
        int err;
@@ -4002,12 +4001,12 @@ 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, &size, INT_MAX,
+       err = kernel_read_file_from_fd(fd, &hdr, INT_MAX,
                                       READING_MODULE);
-       if (err)
+       if (err < 0)
                return err;
        info.hdr = hdr;
-       info.len = size;
+       info.len = err;
return load_module(&info, uargs, flags);
  }
diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
index f8869be45d8f..97661ffabc4e 100644
--- a/security/integrity/digsig.c
+++ b/security/integrity/digsig.c
@@ -171,16 +171,17 @@ int __init integrity_add_key(const unsigned int id, const 
void *data,
  int __init integrity_load_x509(const unsigned int id, const char *path)
  {
        void *data = NULL;
-       loff_t size;
+       size_t size;
        int rc;
        key_perm_t perm;
- rc = kernel_read_file_from_path(path, &data, &size, 0,
+       rc = kernel_read_file_from_path(path, &data, 0,
                                        READING_X509_CERTIFICATE);
        if (rc < 0) {
                pr_err("Unable to open file: %s (%d)", path, rc);
                return rc;
        }
+       size = rc;
perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW | KEY_USR_READ; diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index e13ffece3726..9ba145d3d6d9 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -275,7 +275,7 @@ static ssize_t ima_read_policy(char *path)
  {
        void *data = NULL;
        char *datap;
-       loff_t size;
+       size_t size;
        int rc, pathlen = strlen(path);
char *p;
@@ -284,11 +284,12 @@ static ssize_t ima_read_policy(char *path)
        datap = path;
        strsep(&datap, "\n");
- rc = kernel_read_file_from_path(path, &data, &size, 0, READING_POLICY);
+       rc = kernel_read_file_from_path(path, &data, 0, READING_POLICY);
        if (rc < 0) {
                pr_err("Unable to open file: %s (%d)", path, rc);
                return rc;
        }
+       size = rc;
datap = data;
        while (size > 0 && (p = strsep(&datap, "\n"))) {

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