CVE-2022-40307 (published 2022-09-09T05:15Z)

An issue was discovered in the Linux kernel through 5.19.8. drivers/firmware/efi/capsule-loader.c has a race condition with a resultant use-after-free.

CVSS v3 base score: 4.7, MEDIUM (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-362
cwe_name: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
description: The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.
extended_description: 
            This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider.
            A race condition occurs within concurrent environments, and is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc.
            A race condition violates these properties, which are closely related:
               
                  Exclusivity - the code sequence is given exclusive access to the shared resource, i.e., no other code sequence can modify properties of the shared resource before the original sequence has completed execution.
                  Atomicity - the code sequence is behaviorally atomic, i.e., no other thread or process can concurrently execute the same sequence of instructions (or a subset) against the same resource.
               
            A race condition exists when an "interfering code sequence" can still access the shared resource, violating exclusivity. Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single "x++" statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x).
            The interfering code sequence could be "trusted" or "untrusted." A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Hyunwoo Kim
author_date: 2022-09-07 09:07:14-07:00
msg: efi: capsule-loader: Fix use-after-free in efi_capsule_write

A race condition may occur if the user calls close() on another thread
during a write() operation on the device node of the efi capsule.

This is a race condition that occurs between the efi_capsule_write() and
efi_capsule_flush() functions of efi_capsule_fops, which ultimately
results in UAF.

So, the page freeing process is modified to be done in
efi_capsule_release() instead of efi_capsule_flush().

Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Link: https://lore.kernel.org/all/20220907102920.GA88602@ubuntu/
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: capsule-loader.c
change_type: ModificationType.MODIFY
diff: @@ -242,29 +242,6 @@ static ssize_t efi_capsule_write(struct file *file, const char __user *buff,
 	return ret;
 }
 
-/**
- * efi_capsule_flush - called by file close or file flush
- * @file: file pointer
- * @id: not used
- *
- *	If a capsule is being partially uploaded then calling this function
- *	will be treated as upload termination and will free those completed
- *	buffer pages and -ECANCELED will be returned.
- **/
-static int efi_capsule_flush(struct file *file, fl_owner_t id)
-{
-	int ret = 0;
-	struct capsule_info *cap_info = file->private_data;
-
-	if (cap_info->index > 0) {
-		pr_err("capsule upload not complete\n");
-		efi_free_all_buff_pages(cap_info);
-		ret = -ECANCELED;
-	}
-
-	return ret;
-}
-
 /**
  * efi_capsule_release - called by file close
  * @inode: not used
@@ -277,6 +254,13 @@ static int efi_capsule_release(struct inode *inode, struct file *file)
 {
 	struct capsule_info *cap_info = file->private_data;
 
+	if (cap_info->index > 0 &&
+	    (cap_info->header.headersize == 0 ||
+	     cap_info->count < cap_info->total_size)) {
+		pr_err("capsule upload not complete\n");
+		efi_free_all_buff_pages(cap_info);
+	}
+
 	kfree(cap_info->pages);
 	kfree(cap_info->phys);
 	kfree(file->private_data);
@@ -324,7 +308,6 @@ static const struct file_operations efi_capsule_fops = {
 	.owner = THIS_MODULE,
 	.open = efi_capsule_open,
 	.write = efi_capsule_write,
-	.flush = efi_capsule_flush,
 	.release = efi_capsule_release,
 	.llseek = no_llseek,
 };

programming_language: C