[PATCH v3 1/2] liveupdate: prevent double management of files

[Pasha Tatashin <pasha.tatashin@soleen.com>]

Currently, LUO does not prevent the same file from being managed twice
across different active sessions.

Use a global xarray luo_preserved_files to keep track of file
pointers being preserved by LUO. Update luo_preserve_file() to check and
insert the file pointer into this xarray when it is preserved, and
erase it in luo_file_unpreserve_files() when it is released.

This ensures that the same file (struct file) cannot be managed by
multiple sessions. If another session attempts to preserve an already
managed file, it will now fail with -EBUSY.

Acked-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 kernel/liveupdate/luo_file.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index a38ea4975824..d1bb4213fd14 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -110,11 +110,15 @@
 #include <linux/sizes.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/xarray.h>
 #include "luo_internal.h"
 
 static DECLARE_RWSEM(luo_file_handler_lock);
 static LIST_HEAD(luo_file_handler_list);
 
+/* Keep track of files being preserved by LUO */
+static DEFINE_XARRAY(luo_preserved_files);
+
 /* 2 4K pages, give space for 128 files per file_set */
 #define LUO_FILE_PGCNT		2ul
 #define LUO_FILE_MAX							\
@@ -249,6 +253,7 @@ static bool luo_token_is_used(struct luo_file_set *file_set, u64 token)
  * Context: Can be called from an ioctl handler during normal system operation.
  * Return: 0 on success. Returns a negative errno on failure:
  *         -EEXIST if the token is already used.
+ *         -EBUSY if the file descriptor is already preserved by another session.
  *         -EBADF if the file descriptor is invalid.
  *         -ENOSPC if the file_set is full.
  *         -ENOENT if no compatible handler is found.
@@ -277,6 +282,11 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	if (err)
 		goto  err_fput;
 
+	err = xa_insert(&luo_preserved_files, (unsigned long)file,
+			file, GFP_KERNEL);
+	if (err)
+		goto err_free_files_mem;
+
 	err = -ENOENT;
 	scoped_guard(rwsem_read, &luo_file_handler_lock) {
 		list_private_for_each_entry(fh, &luo_file_handler_list, list) {
@@ -289,11 +299,11 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 
 	/* err is still -ENOENT if no handler was found */
 	if (err)
-		goto err_free_files_mem;
+		goto err_erase_xa;
 
 	err = luo_flb_file_preserve(fh);
 	if (err)
-		goto err_free_files_mem;
+		goto err_erase_xa;
 
 	luo_file = kzalloc_obj(*luo_file);
 	if (!luo_file) {
@@ -323,6 +333,8 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	kfree(luo_file);
 err_flb_unpreserve:
 	luo_flb_file_unpreserve(fh);
+err_erase_xa:
+	xa_erase(&luo_preserved_files, (unsigned long)file);
 err_free_files_mem:
 	luo_free_files_mem(file_set);
 err_fput:
@@ -366,6 +378,7 @@ void luo_file_unpreserve_files(struct luo_file_set *file_set)
 		luo_file->fh->ops->unpreserve(&args);
 		luo_flb_file_unpreserve(luo_file->fh);
 
+		xa_erase(&luo_preserved_files, (unsigned long)luo_file->file);
 		list_del(&luo_file->list);
 		file_set->count--;
 
@@ -609,6 +622,10 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
 	luo_file->file = args.file;
 	/* Get reference so we can keep this file in LUO until finish */
 	get_file(luo_file->file);
+
+	WARN_ON(xa_insert(&luo_preserved_files, (unsigned long)luo_file->file,
+			  luo_file->file, GFP_KERNEL));
+
 	*filep = luo_file->file;
 	luo_file->retrieve_status = 1;
 
@@ -704,8 +721,11 @@ int luo_file_finish(struct luo_file_set *file_set)
 
 		luo_file_finish_one(file_set, luo_file);
 
-		if (luo_file->file)
+		if (luo_file->file) {
+			xa_erase(&luo_preserved_files,
+				 (unsigned long)luo_file->file);
 			fput(luo_file->file);
+		}
 		list_del(&luo_file->list);
 		file_set->count--;
 		mutex_destroy(&luo_file->mutex);
-- 
2.43.0