CVE-2025-40072

What is known

In the Linux kernel, the following vulnerability has been resolved: fanotify: Validate the return value of mnt_ns_from_dentry() before dereferencing The function do_fanotify_mark() does not validate if mnt_ns_from_dentry() returns NULL before dereferencing mntns->user_ns. This causes a NULL pointer dereference in do_fanotify_mark() if the path is not a mount namespace object. Fix this by checking mnt_ns_from_dentry()'s return value before dereferencing it. Before the patch $ gcc fanotify_nullptr.c -o fanotify_nullptr $ mkdir A $ ./fanotify_nullptr Fanotify fd: 3 fanotify_mark: Operation not permitted $ unshare -Urm Fanotify fd: 3 Killed int main(void){ int ffd; ffd = fanotify_init(FAN_CLASS_NOTIF | FAN_REPORT_MNT, 0); if(ffd < 0){ perror("fanotify_init"); exit(EXIT_FAILURE); } printf("Fanotify fd: %d\n",ffd); if(fanotify_mark(ffd, FAN_MARK_ADD | FAN_MARK_MNTNS, FAN_MNT_ATTACH, AT_FDCWD, "A") < 0){ perror("fanotify_mark"); exit(EXIT_FAILURE); } return 0; } After the patch $ gcc fanotify_nullptr.c -o fanotify_nullptr $ mkdir A $ ./fanotify_nullptr Fanotify fd: 3 fanotify_mark: Operation not permitted $ unshare -Urm Fanotify fd: 3 fanotify_mark: Invalid argument [ 25.694973] BUG: kernel NULL pointer dereference, address: 0000000000000038 [ 25.695006] #PF: supervisor read access in kernel mode [ 25.695012] #PF: error_code(0x0000) - not-present page [ 25.695017] PGD 109a30067 P4D 109a30067 PUD 142b46067 PMD 0 [ 25.695025] Oops: Oops: 0000 [#1] SMP NOPTI [ 25.695032] CPU: 4 UID: 1000 PID: 1478 Comm: fanotify_nullpt Not tainted 6.17.0-rc4 #1 PREEMPT(lazy) [ 25.695040] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 [ 25.695049] RIP: 0010:do_fanotify_mark+0x817/0x950 [ 25.695066] Code: 04 00 00 e9 45 fd ff ff 48 8b 7c 24 48 4c 89 54 24 18 4c 89 5c 24 10 4c 89 0c 24 e8 b3 11 fc ff 4c 8b 54 24 18 4c 8b 5c 24 10 <48> 8b 78 38 4c 8b 0c 24 49 89 c4 e9 13 fd ff ff 8b 4c 24 28 85 c9 [ 25.695081] RSP: 0018:ffffd31c469e3c08 EFLAGS: 00010203 [ 25.695104] RAX: 0000000000000000 RBX: 0000000001000000 RCX: ffff8eb48aebd220 [ 25.695110] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8eb4835e8180 [ 25.695115] RBP: 0000000000000111 R08: 0000000000000000 R09: 0000000000000000 [ 25.695142] R10: ffff8eb48a7d56c0 R11: ffff8eb482bede00 R12: 00000000004012a7 [ 25.695148] R13: 0000000000000110 R14: 0000000000000001 R15: ffff8eb48a7d56c0 [ 25.695154] FS: 00007f8733bda740(0000) GS:ffff8eb61ce5f000(0000) knlGS:0000000000000000 [ 25.695162] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 25.695170] CR2: 0000000000000038 CR3: 0000000136994006 CR4: 00000000003706f0 [ 25.695201] Call Trace: [ 25.695209] <TASK> [ 25.695215] __x64_sys_fanotify_mark+0x1f/0x30 [ 25.695222] do_syscall_64+0x82/0x2c0 ...

Business impact

Successful exploitation of CVE-2025-40072, a reported vulnerability affecting the affected product, may affect the confidentiality, integrity or availability of the vulnerable environment. The exact impact depends on the installed version, exposed interfaces and deployment configuration.

Recommended administrator action

Confirm whether the affected product is present and compare installed versions with the vendor advisory and NVD record. Apply the vendor patch or documented mitigation; until remediation is complete, reduce exposure of affected interfaces, review relevant logs and monitor for indicators of exploitation. DataHouse can support version verification, managed patching, network exposure reduction, log review and backup validation for dedicated, cloud and colocated environments.

Sources

• NVD
• Reference
• Reference