rds: ib: Clear the sg list when mapping an MR fails

Overview

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

rds: ib: Clear the sg list when mapping an MR fails

rds_ib_map_frmr() stores the caller's scatterlist in the MR before DMA mapping and registration can fail. On failure, __rds_rdma_map() unpins the pages and frees the scatterlist, but rds_ib_free_frmr() can still return the MR to the pool with the stale pointer set.

This leaves the pool with a dangling scatterlist and can lead to local privilege escalation. KASAN detects the resulting use-after-free when the MR is later torn down:

BUG: KASAN: slab-use-after-free in __rds_ib_teardown_mr Read of size 8

Call Trace: __rds_ib_teardown_mr rds_ib_unreg_frmr rds_ib_flush_mr_pool rds_ib_flush_mrs rds_free_mr rds_setsockopt

Store the scatterlist in the MR only after DMA mapping succeeds. If DMA mapping fails, return directly while the MR fields remain clear; the caller keeps ownership of the scatterlist and its pinned pages. If a later registration step fails, unmap the scatterlist and clear the MR fields before returning.

Affected

• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < 1be3211e6ac77adbb1eac01314d989d243b32c59
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < c42d316163f89cd23de2f3e24558177a8c29bad8
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < 8dca3c81344532a7f05edb3d12f31f3009410a90
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < 49ba5ed0129906e0362c2e4b5e21c89b2a41e115
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < 4468df5bcdef959fd96494e9968f323561a45f4c
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < e2ee0616260080376123997488b5cf8a3870b8d9
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < b36d32f30c3f1e58e3a5ae79d0f52836a316b36e
• Linux >= 1659185fb4d0025835eb2058a141f0746c5cab00 < 58eb1b3325edac42dc6df72c80962bd53a3c8ca7
• Linux 4.6

Remediation

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