net: xps: reject an out of range traffic class

Overview

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

net: xps: reject an out of range traffic class

Only the entries below dev->num_tc are valid in dev->tc_to_txq[], and dev->prio_tc_map[] may only name classes below it. netdev_set_num_tc() lowers dev->num_tc without touching either array.

netdev_txq_to_tc() walks all TC_MAX_QUEUE slots and netdev_get_prio_tc_map() returns the entry as it stands, so a leftover entry is handed out as a traffic class >= dev->num_tc. Taking that class from netdev_txq_to_tc(), __netif_set_xps_queue() rejects only a negative one and indexes an XPS map sized for dev->num_tc classes:

tci = j * num_tc + tc;
RCU_INIT_POINTER(new_dev_maps->attr_map[tci], map);

attr_map[] holds nr_ids * num_tc entries and j runs over the ids named in the mask, so a class that is not below num_tc pushes tci past the end of the map for the last ids and the store overruns it.

Any caller that lowers num_tc leaves such entries behind, and mqprio_destroy() tears down with netdev_set_num_tc(dev, 0) rather than netdev_reset_tc(). After mqprio with 8 classes then 1, tc_to_txq[1..7] still describe txq 1..7. The splat is from an XPS write to txq 2 on a veth with 8 rx queues: attr_map[] has 8 * 1 entries, tci = j + 2, and j == 6 stores one past the end of the 88-byte map:

BUG: KASAN: slab-out-of-bounds in __netif_set_xps_queue (net/core/dev.c:2954) Write of size 8 at addr ffff88813016bc58 by task xps_oob/634 __netif_set_xps_queue (net/core/dev.c:2954) xps_rxqs_store (net/core/net-sysfs.c:1880) netdev_queue_attr_store (net/core/net-sysfs.c:1390) Allocated by task 634: __kmalloc_noprof (mm/slub.c:5439) __netif_set_xps_queue (net/core/dev.c:2937) The buggy address is located 0 bytes to the right of allocated 88-byte region [ffff88813016bc00, ffff88813016bc58)

Reject a class the map has no room for.

Affected

• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 967e10f40a0c6732db299cbe001df0e859196055
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 1cb8e40525a72c9f1e1cf94c68c172b3b9bbdc81
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 6ea8f643053f33622f9116e4e1db58306ece45e3
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 9e841723ba482d41ecbf90241c756a16cdfea949
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < eff227a3cb4d0089fbb85c73480bf8abf2e5ae7f
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 2cc1c3977acbffc417fb5b57699d1df3dcffb5fd
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 930318290d8509e864c015fe6c9239470b3c579c
• Linux >= 184c449f91fef521042970cca46bd5cdfc0e3a37 < 4da3b7b8b50f3e2fde54a4c18a82a8e3f6223910
• Linux 4.10

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.