Description

In the Linux kernel, the following vulnerability has been resolved: net/smc: avoid NULL deref of conn->lnk in smc_msg_event tracepoint The smc_msg_event tracepoint class, shared by smc_tx_sendmsg and smc_rx_recvmsg, unconditionally dereferences smc->conn.lnk: __string(name, smc->conn.lnk->ibname) conn->lnk is only set for SMC-R; for SMC-D it is NULL. Other code on these paths already handles this (e.g. !conn->lnk in SMC_STAT_RMB_TX_SIZE_SMALL()). With the tracepoint enabled, the first sendmsg()/recvmsg() on an SMC-D socket crashes: Oops: general protection fault, probably for non-canonical address KASAN: null-ptr-deref in range [...] RIP: 0010:strlen+0x1e/0xa0 Call Trace: trace_event_raw_event_smc_msg_event (net/smc/smc_tracepoint.h:44) smc_rx_recvmsg (net/smc/smc_rx.c:515) smc_recvmsg (net/smc/af_smc.c:2859) __sys_recvfrom (net/socket.c:2315) __x64_sys_recvfrom (net/socket.c:2326) do_syscall_64 The faulting address 0x3e0 is offsetof(struct smc_link, ibname), confirming the NULL ->lnk deref. Enabling the tracepoint requires root, but the trigger itself is unprivileged: socket(AF_SMC, ...) has no capability check, and SMC-D negotiation needs no admin step on s390 or on x86 with the loopback ISM device loaded. Log an empty device name for SMC-D instead of dereferencing NULL.

References 6

• git.kernel.org https://git.kernel.org/stable/c/561cf66fa9b6c86dfe4e687d2d1aeaaa6739917f
• git.kernel.org https://git.kernel.org/stable/c/68200112534bb2acd1d7117dc2d5c124868d866d
• git.kernel.org https://git.kernel.org/stable/c/720c76b930c52cd58f50eb6b10569d03dccc7959
• git.kernel.org https://git.kernel.org/stable/c/7bf563badd37cb796df5477d2b78bb64148a1268
• git.kernel.org https://git.kernel.org/stable/c/b706d6d76a2a2793fe5ad0fbc2a75b6a460094ef
• git.kernel.org https://git.kernel.org/stable/c/d2ea0b8aef8746e147602eac87ca8538f4bc7e66

Remediation