Re: [PATCH 06/13] fs/kernel_read_file: Remove redundant size argument

[Scott Branden <scott.branden@xxxxxxxxxxxx>]

On 2020-07-17 12:04 p.m., Scott Branden wrote:
> 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?
Actually, this change looks ok dealing with the size.  I'll look at the 
rest.
> > code, with callers adjusted. (VFS reads already cannot be larger than
> > INT_MAX.)
> >
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> >   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"))) {