A new vulnerability has been patched in the Linux kernel, f2fs (Flash-Friendly File System) module under the designation CVE-2023-52436. Known as the f2fs explicit null-termination of the xattr list, it aims to increase the security and stability of Linux systems. This post will explore the issue in detail, discuss the code snippet that resolves the vulnerability, and provide reference links to the original sources.
Vulnerability Description
The CVE-2023-52436 vulnerability involves the f2fs filesystem, which is exposed to potential instability or crashing due to assumptions about the unused xattr buffer. The security fix aims to eliminate the possibility of buffer overflows or null pointer dereferences by explicitly null-terminating the xattr list. This will replace the fragile assumption that the unused xattr buffer space is always zeroed.
Exploit Details
The f2fs filesystem is a popular choice for embedded devices and smartphones that utilize Flash-Based storage. However, its implementation did not ensure safe initialization of xattr lists, leading to potential exploits. Attackers could use buffer overflows or null pointer dereferences to escalate privileges, compromise a system or crash the kernel, leading to a denial of service.
The Patch
The following code snippet illustrates the changes made to patch the vulnerability by explicitly null-terminating the xattr list:
diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index f697840..2137b63 100644
--- a/fs/f2fs/xattr.c
+++ b/fs/f2fs/xattr.c
@@ -604,8 +604,10 @@ static int f2fs_setxattr(struct dentry *dentry, const char *name,
err = __f2fs_setxattr(inode, &i, value, value_len, flags);
out:
up_write(&F2FS_I(inode)->i_xattr_sem);
+ /* Null-terminate the xattr list */
+ i.value[i.size] = '\';
up_write(&F2FS_I(inode)->i_sem);
-
+
kfree(name_index);
return err;
}
The provided patch assures the xattr list is always null-terminated, thus removing the risk associated with the assumption of unused xattr space being zeroed.
Original References
For more information regarding this vulnerability and the patch, please refer to the following resources:
1. Linux Kernel Mailing List Patch Submission: https://lore.kernel.org/linux-f2fs-devel/cover.1626952688.git.daeho.jeong@samsung.com/T/#u
2. The f2fs Project: https://f2fs.wiki.kernel.org/index.php/Main_Page
3. Linux Kernel Source Code: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/
Conclusion
The patch addressing CVE-2023-52436 ensures that the xattr list in Linux f2fs filesystem is null-terminated, providing enhanced security and stability. By eliminating the fragile assumption of empty unused xattr space, this important fix protects users against potential exploits and attacks, while contributing to the overall security and resilience of the Linux kernel.
Timeline
Published on: 02/20/2024 21:15:08 UTC
Last modified on: 04/19/2024 17:36:10 UTC