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authorKees Cook <keescook@chromium.org>2020-10-02 20:38:25 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-10-05 14:37:04 +0300
commit0fa8e084648779eeb8929ae004301b3acf3bad84 (patch)
treeebfed647c8f2a43a0967ba127c7e75df36909cba /fs/kernel_read_file.c
parent34736daeecd1608bee21e3bf5170cd4c95143109 (diff)
downloadlinux-0fa8e084648779eeb8929ae004301b3acf3bad84.tar.xz
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>
Diffstat (limited to 'fs/kernel_read_file.c')
-rw-r--r--fs/kernel_read_file.c78
1 files changed, 54 insertions, 24 deletions
diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c
index d73bc3fa710a..90d255fbdd9b 100644
--- 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;