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

SUNRPC: Fix RPC client cleaned up the freed pipefs dentries

RPC client pipefs dentries cleanup is in separated rpc_remove_pipedir() workqueue,which takes care about pipefs superblock locking. In some special scenarios, when kernel frees the pipefs sb of the current client and immediately alloctes a new pipefs sb, rpc_remove_pipedir function would misjudge the existence of pipefs sb which is not the one it used to hold. As a result, the rpc_remove_pipedir would clean the released freed pipefs dentries.

To fix this issue, rpc_remove_pipedir should check whether the current pipefs sb is consistent with the original pipefs sb.

This error can be catched by KASAN:

[ 250.497700] BUG: KASAN: slab-use-after-free in dget_parent+0x195/0x200 [ 250.498315] Read of size 4 at addr ffff88800a2ab804 by task kworker/0:18/106503 [ 250.500549] Workqueue: events rpc_free_client_work [ 250.501001] Call Trace: [ 250.502880] kasan_report+0xb6/0xf0 [ 250.503209] ? dget_parent+0x195/0x200 [ 250.503561] dget_parent+0x195/0x200 [ 250.503897] ? __pfx_rpc_clntdir_depopulate+0x10/0x10 [ 250.504384] rpc_rmdir_depopulate+0x1b/0x90 [ 250.504781] rpc_remove_client_dir+0xf5/0x150 [ 250.505195] rpc_free_client_work+0xe4/0x230 [ 250.505598] process_one_work+0x8ee/0x13b0 … [ 22.039056] Allocated by task 244: [ 22.039390] kasan_save_stack+0x22/0x50 [ 22.039758] kasan_set_track+0x25/0x30 [ 22.040109] __kasan_slab_alloc+0x59/0x70 [ 22.040487] kmem_cache_alloc_lru+0xf0/0x240 [ 22.040889] __d_alloc+0x31/0x8e0 [ 22.041207] d_alloc+0x44/0x1f0 [ 22.041514] __rpc_lookup_create_exclusive+0x11c/0x140 [ 22.041987] rpc_mkdir_populate.constprop.0+0x5f/0x110 [ 22.042459] rpc_create_client_dir+0x34/0x150 [ 22.042874] rpc_setup_pipedir_sb+0x102/0x1c0 [ 22.043284] rpc_client_register+0x136/0x4e0 [ 22.043689] rpc_new_client+0x911/0x1020 [ 22.044057] rpc_create_xprt+0xcb/0x370 [ 22.044417] rpc_create+0x36b/0x6c0 … [ 22.049524] Freed by task 0: [ 22.049803] kasan_save_stack+0x22/0x50 [ 22.050165] kasan_set_track+0x25/0x30 [ 22.050520] kasan_save_free_info+0x2b/0x50 [ 22.050921] __kasan_slab_free+0x10e/0x1a0 [ 22.051306] kmem_cache_free+0xa5/0x390 [ 22.051667] rcu_core+0x62c/0x1930 [ 22.051995] __do_softirq+0x165/0x52a [ 22.052347] [ 22.052503] Last potentially related work creation: [ 22.052952] kasan_save_stack+0x22/0x50 [ 22.053313] __kasan_record_aux_stack+0x8e/0xa0 [ 22.053739] __call_rcu_common.constprop.0+0x6b/0x8b0 [ 22.054209] dentry_free+0xb2/0x140 [ 22.054540] __dentry_kill+0x3be/0x540 [ 22.054900] shrink_dentry_list+0x199/0x510 [ 22.055293] shrink_dcache_parent+0x190/0x240 [ 22.055703] do_one_tree+0x11/0x40 [ 22.056028] shrink_dcache_for_umount+0x61/0x140 [ 22.056461] generic_shutdown_super+0x70/0x590 [ 22.056879] kill_anon_super+0x3a/0x60 [ 22.057234] rpc_kill_sb+0x121/0x200

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/17866066b8ac1cc38fb449670bc15dc9fee4b40a
• https://git.kernel.org/stable/c/194454afa6aa9d6ed74f0c57127bc8beb27c20df
• https://git.kernel.org/stable/c/1cdb52ffd6600a37bd355d8dce58ecd03e55e618
• https://git.kernel.org/stable/c/7749fd2dbef72a52b5c9ffdbf877691950ed4680
• https://git.kernel.org/stable/c/7d61d1da2ed1f682c41cae0c8d4719cdaccee5c5
• https://git.kernel.org/stable/c/bfca5fb4e97c46503ddfc582335917b0cc228264
• https://git.kernel.org/stable/c/cc2e7ebbeb1d0601f7f3c8d93b78fcc03a95e44a
• https://git.kernel.org/stable/c/dedf2a0eb9448ae73b270743e6ea9b108189df46
• https://git.kernel.org/stable/c/17866066b8ac1cc38fb449670bc15dc9fee4b40a
• https://git.kernel.org/stable/c/194454afa6aa9d6ed74f0c57127bc8beb27c20df
• https://git.kernel.org/stable/c/1cdb52ffd6600a37bd355d8dce58ecd03e55e618
• https://git.kernel.org/stable/c/7749fd2dbef72a52b5c9ffdbf877691950ed4680
• https://git.kernel.org/stable/c/7d61d1da2ed1f682c41cae0c8d4719cdaccee5c5
• https://git.kernel.org/stable/c/bfca5fb4e97c46503ddfc582335917b0cc228264
• https://git.kernel.org/stable/c/cc2e7ebbeb1d0601f7f3c8d93b78fcc03a95e44a
• https://git.kernel.org/stable/c/dedf2a0eb9448ae73b270743e6ea9b108189df46