CVE-2021-47563

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

ice: avoid bpf_prog refcount underflow

Ice driver has the routines for managing XDP resources that are shared between ndobpf op and VSI rebuild flow. The latter takes place for example when user changes queue count on an interface via ethtool's setchannels().

There is an issue around the bpfprog refcounting when VSI is being rebuilt - since icepreparexdprings() is called with vsi->xdpprog as an argument that is used later on by icevsiassignbpfprog(), same bpfprog pointers are swapped with each other. Then it is also interpreted as an 'oldprog' which in turn causes us to call bpfprog_put on it that will decrement its refcount.

Below splat can be interpreted in a way that due to zero refcount of a bpf_prog it is wiped out from the system while kernel still tries to refer to it:

[ 481.069429] BUG: unable to handle page fault for address: ffffc9000640f038 [ 481.077390] #PF: supervisor read access in kernel mode [ 481.083335] #PF: errorcode(0x0000) - not-present page [ 481.089276] PGD 100000067 P4D 100000067 PUD 1001cb067 PMD 106d2b067 PTE 0 [ 481.097141] Oops: 0000 [#1] PREEMPT SMP PTI [ 481.101980] CPU: 12 PID: 3339 Comm: sudo Tainted: G OE 5.15.0-rc5+ #1 [ 481.110840] Hardware name: Intel Corp. GRANTLEY/GRANTLEY, BIOS GRRFCRB1.86B.0276.D07.1605190235 05/19/2016 [ 481.122021] RIP: 0010:devxdpprogid+0x25/0x40 [ 481.127265] Code: 80 00 00 00 00 0f 1f 44 00 00 89 f6 48 c1 e6 04 48 01 fe 48 8b 86 98 08 00 00 48 85 c0 74 13 48 8b 50 18 31 c0 48 85 d2 74 07 <48> 8b 42 38 8b 40 20 c3 48 8b 96 90 08 00 00 eb e8 66 2e 0f 1f 84 [ 481.148991] RSP: 0018:ffffc90007b63868 EFLAGS: 00010286 [ 481.155034] RAX: 0000000000000000 RBX: ffff889080824000 RCX: 0000000000000000 [ 481.163278] RDX: ffffc9000640f000 RSI: ffff889080824010 RDI: ffff889080824000 [ 481.171527] RBP: ffff888107af7d00 R08: 0000000000000000 R09: ffff88810db5f6e0 [ 481.179776] R10: 0000000000000000 R11: ffff8890885b9988 R12: ffff88810db5f4bc [ 481.188026] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 481.196276] FS: 00007f5466d5bec0(0000) GS:ffff88903fb00000(0000) knlGS:0000000000000000 [ 481.205633] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 481.212279] CR2: ffffc9000640f038 CR3: 000000014429c006 CR4: 00000000003706e0 [ 481.220530] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 481.228771] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 481.237029] Call Trace: [ 481.239856] rtnlfillifinfo+0x768/0x12e0 [ 481.244602] rtnldumpifinfo+0x525/0x650 [ 481.249246] ? allocskb+0xa5/0x280 [ 481.253484] netlinkdump+0x168/0x3c0 [ 481.257725] netlinkrecvmsg+0x21e/0x3e0 [ 481.262263] _sysrecvmsg+0x87/0x170 [ 481.266707] ? mightfault+0x20/0x30 [ 481.271046] ? copyfromuser+0x66/0xa0 [ 481.275591] ? iovecfromuser+0xf6/0x1c0 [ 481.280226] _sysrecvmsg+0x82/0x100 [ 481.284566] ? socksendmsg+0x5e/0x60 [ 481.288791] ? _syssendto+0xee/0x150 [ 481.293129] _sysrecvmsg+0x56/0xa0 [ 481.297267] dosyscall64+0x3b/0xc0 [ 481.301395] entrySYSCALL64afterhwframe+0x44/0xae [ 481.307238] RIP: 0033:0x7f5466f39617 [ 481.311373] Code: 0c 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb bd 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2f 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 [ 481.342944] RSP: 002b:00007ffedc7f4308 EFLAGS: 00000246 ORIGRAX: 000000000000002f [ 481.361783] RAX: ffffffffffffffda RBX: 00007ffedc7f5460 RCX: 00007f5466f39617 [ 481.380278] RDX: 0000000000000000 RSI: 00007ffedc7f5360 RDI: 0000000000000003 [ 481.398500] RBP: 00007ffedc7f53f0 R08: 0000000000000000 R09: 000055d556f04d50 [ 481.416463] R10: 0000000000000077 R11: 0000000000000246 R12: 00007ffedc7f5360 [ 481.434131] R13: 00007ffedc7f5350 R14: 00007ffedc7f5344 R15: 0000000000000e98 [ 481.451520] Modules linked in: ice ---truncated---