CVE-2024-35870

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

smb: client: fix UAF in smb2reconnectserver()

The UAF bug is due to smb2reconnectserver() accessing a session that is already being teared down by another thread that is executing _cifsputsmbses(). This can happen when (a) the client has connection to the server but no session or (b) another thread ends up setting @ses->sesstatus again to something different than SESEXITING.

To fix this, we need to make sure to unconditionally set @ses->sesstatus to SESEXITING and prevent any other threads from setting a new status while we're still tearing it down.

The following can be reproduced by adding some delay to right after the ipc is freed in _cifsputsmbses() - which will give smb2reconnectserver() worker a chance to run and then accessing @ses->ipc:

kinit ... mount.cifs //srv/share /mnt/1 -o sec=krb5,nohandlecache,echointerval=10 [disconnect srv] ls /mnt/1 &>/dev/null sleep 30 kdestroy [reconnect srv] sleep 10 umount /mnt/1 ... CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed CIFS: VFS: \srv Send error in SessSetup = -126 CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed CIFS: VFS: \srv Send error in SessSetup = -126 general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP NOPTI CPU: 3 PID: 50 Comm: kworker/3:1 Not tainted 6.9.0-rc2 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39 04/01/2014 Workqueue: cifsiod smb2reconnect_server [cifs] RIP: 0010:__listdelentryvalidorreport+0x33/0xf0 Code: 4f 08 48 85 d2 74 42 48 85 c9 74 59 48 b8 00 01 00 00 00 00 ad de 48 39 c2 74 61 48 b8 22 01 00 00 00 00 74 69 <48> 8b 01 48 39 f8 75 7b 48 8b 72 08 48 39 c6 0f 85 88 00 00 00 b8 RSP: 0018:ffffc900001bfd70 EFLAGS: 00010a83 RAX: dead000000000122 RBX: ffff88810da53838 RCX: 6b6b6b6b6b6b6b6b RDX: 6b6b6b6b6b6b6b6b RSI: ffffffffc02f6878 RDI: ffff88810da53800 RBP: ffff88810da53800 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000001 R12: ffff88810c064000 R13: 0000000000000001 R14: ffff88810c064000 R15: ffff8881039cc000 FS: 0000000000000000(0000) GS:ffff888157c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fe3728b1000 CR3: 000000010caa4000 CR4: 0000000000750ef0 PKRU: 55555554 Call Trace: <TASK> ? dieaddr+0x36/0x90 ? excgeneralprotection+0x1c1/0x3f0 ? asmexcgeneral_protection+0x26/0x30 ? __listdelentryvalidor_report+0x33/0xf0 __cifsputsmbses+0x1ae/0x500 [cifs] smb2reconnectserver+0x4ed/0x710 [cifs] processonework+0x205/0x6b0 workerthread+0x191/0x360 ? __pfxworkerthread+0x10/0x10 kthread+0xe2/0x110 ? __pfxkthread+0x10/0x10 retfrom_fork+0x34/0x50 ? __pfxkthread+0x10/0x10 retfromforkasm+0x1a/0x30 </TASK>