CVE-2022-50214

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

coresight: Clear the connection field properly

coresight devices track their connections (output connections) and hold a reference to the fwnode. When a device goes away, we walk through the devices on the coresight bus and make sure that the references are dropped. This happens both ways: a) For all output connections from the device, drop the reference to the target device via coresight_release_platform_data()

b) Iterate over all the devices on the coresight bus and drop the reference to fwnode if this device is the target of the output connection, via coresight_remove_conns()->coresight_remove_match().

However, the coresight_remove_match() doesnt clear the fwnode field, after dropping the reference, this causes use-after-free and additional refcount drops on the fwnode.

e.g., if we have two devices, A and B, with a connection, A -> B. If we remove B first, B would clear the reference on B, from A via coresight_remove_match(). But when A is removed, it still has a connection with fwnode still pointing to B. Thus it tries to drops the reference in coresight_release_platform_data(), raising the bells like :

[ 91.990153] ————[ cut here ]———— [ 91.990163] refcount_t: addition on 0; use-after-free. [ 91.990212] WARNING: CPU: 0 PID: 461 at lib/refcount.c:25 refcount_warn_saturate+0xa0/0x144 [ 91.990260] Modules linked in: coresight_funnel coresight_replicator coresight_etm4x(-) crct10dif_ce coresight ip_tables x_tables ipv6 [last unloaded: coresight_cpu_debug] [ 91.990398] CPU: 0 PID: 461 Comm: rmmod Tainted: G W T 5.19.0-rc2+ #53 [ 91.990418] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Feb 1 2019 [ 91.990434] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=–) [ 91.990454] pc : refcount_warn_saturate+0xa0/0x144 [ 91.990476] lr : refcount_warn_saturate+0xa0/0x144 [ 91.990496] sp : ffff80000c843640 [ 91.990509] x29: ffff80000c843640 x28: ffff800009957c28 x27: ffff80000c8439a8 [ 91.990560] x26: ffff00097eff1990 x25: ffff8000092b6ad8 x24: ffff00097eff19a8 [ 91.990610] x23: ffff80000c8439a8 x22: 0000000000000000 x21: ffff80000c8439c2 [ 91.990659] x20: 0000000000000000 x19: ffff00097eff1a10 x18: ffff80000ab99c40 [ 91.990708] x17: 0000000000000000 x16: 0000000000000000 x15: ffff80000abf6fa0 [ 91.990756] x14: 000000000000001d x13: 0a2e656572662d72 x12: 657466612d657375 [ 91.990805] x11: 203b30206e6f206e x10: 6f69746964646120 x9 : ffff8000081aba28 [ 91.990854] x8 : 206e6f206e6f6974 x7 : 69646461203a745f x6 : 746e756f63666572 [ 91.990903] x5 : ffff00097648ec58 x4 : 0000000000000000 x3 : 0000000000000027 [ 91.990952] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff00080260ba00 [ 91.991000] Call trace: [ 91.991012] refcount_warn_saturate+0xa0/0x144 [ 91.991034] kobject_get+0xac/0xb0 [ 91.991055] of_node_get+0x2c/0x40 [ 91.991076] of_fwnode_get+0x40/0x60 [ 91.991094] fwnode_handle_get+0x3c/0x60 [ 91.991116] fwnode_get_nth_parent+0xf4/0x110 [ 91.991137] fwnode_full_name_string+0x48/0xc0 [ 91.991158] device_node_string+0x41c/0x530 [ 91.991178] pointer+0x320/0x3ec [ 91.991198] vsnprintf+0x23c/0x750 [ 91.991217] vprintk_store+0x104/0x4b0 [ 91.991238] vprintk_emit+0x8c/0x360 [ 91.991257] vprintk_default+0x44/0x50 [ 91.991276] vprintk+0xcc/0xf0 [ 91.991295] _printk+0x68/0x90 [ 91.991315] of_node_release+0x13c/0x14c [ 91.991334] kobject_put+0x98/0x114 [ 91.991354] of_node_put+0x24/0x34 [ 91.991372] of_fwnode_put+0x40/0x5c [ 91.991390] fwnode_handle_put+0x38/0x50 [ 91.991411] coresight_release_platform_data+0x74/0xb0 [coresight] [ 91.991472] coresight_unregister+0x64/0xcc [coresight] [ 91.991525] etm4_remove_dev+0x64/0x78 [coresight_etm4x] [ 91.991563] etm4_remove_amba+0x1c/0x2c [coresight_etm4x] [ 91.991598] amba_remove+0x3c/0x19c —truncated—

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/2af89ebacf299b7fba5f3087d35e8a286ec33706
• https://git.kernel.org/stable/c/847b9273dd61567fb77617eabc5fa002594db062
• https://git.kernel.org/stable/c/b49b29ee113a87997bcca0bb0585bb46582846c1
• https://git.kernel.org/stable/c/bc57850fcb7e4cb91b6321d0ce83357cefd55c54
• https://git.kernel.org/stable/c/d43e967963c4d1b2b49f894d2f1b12865f87b098
• https://git.kernel.org/stable/c/e9205d8dd1cafb7cff689ef9ddf06276a68f54a4