CVE-2025-68183

Summary

In the Linux kernel, the following vulnerability has been resolved:

ima: don't clear IMA_DIGSIG flag when setting or removing non-IMA xattr

Currently when both IMA and EVM are in fix mode, the IMA signature will be reset to IMA hash if a program first stores IMA signature in security.ima and then writes/removes some other security xattr for the file.

For example, on Fedora, after booting the kernel with "ima_appraise=fix evm=fix ima_policy=appraise_tcb" and installing rpm-plugin-ima, installing/reinstalling a package will not make good reference IMA signature generated. Instead IMA hash is generated,

# getfattr -m - -d -e hex /usr/bin/bash
# file: usr/bin/bash
security.ima=0x0404...

This happens because when setting security.selinux, the IMA_DIGSIG flag that had been set early was cleared. As a result, IMA hash is generated when the file is closed.

Similarly, IMA signature can be cleared on file close after removing security xattr like security.evm or setting/removing ACL.

Prevent replacing the IMA file signature with a file hash, by preventing the IMA_DIGSIG flag from being reset.

Here's a minimal C reproducer which sets security.selinux as the last step which can also replaced by removing security.evm or setting ACL,

#include <stdio.h>
#include <sys/xattr.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

int main() {
    const char* file_path = "/usr/sbin/test_binary";
    const char* hex_string = "030204d33204490066306402304";
    int length = strlen(hex_string);
    char* ima_attr_value;
    int fd;

    fd = open(file_path, O_WRONLY|O_CREAT|O_EXCL, 0644);
    if (fd == -1) {
        perror("Error opening file");
        return 1;
    }

    ima_attr_value = (char*)malloc(length / 2 );
    for (int i = 0, j = 0; i < length; i += 2, j++) {
        sscanf(hex_string + i, "%2hhx", &ima_attr_value[j]);
    }

    if (fsetxattr(fd, "security.ima", ima_attr_value, length/2, 0) == -1) {
        perror("Error setting extended attribute");
        close(fd);
        return 1;
    }

    const char* selinux_value= "system_u:object_r:bin_t:s0";
    if (fsetxattr(fd, "security.selinux", selinux_value, strlen(selinux_value), 0) == -1) {
        perror("Error setting extended attribute");
        close(fd);
        return 1;
    }

    close(fd);

    return 0;
}

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/d2993a7e98eb70c737c6f5365a190e79c72b8407
• https://git.kernel.org/stable/c/edd824eb45e4f7e05ad3ab090dab6dbdb79cd292
• https://git.kernel.org/stable/c/02aa671c08a4834bef5166743a7b88686fbfa023
• https://git.kernel.org/stable/c/88b4cbcf6b041ae0f2fc8a34554a5b6a83a2b7cd

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