net/smc: fix double-free of smc_spd_priv when tee() duplicates splice pipe buffer

Overview

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

net/smc: fix double-free of smc_spd_priv when tee() duplicates splice pipe buffer

smc_rx_splice() allocates one smc_spd_priv per pipe_buffer and stores the pointer in pipe_buffer.private. The pipe_buf_operations for these buffers used .get = generic_pipe_buf_get, which only increments the page reference count when tee(2) duplicates a pipe buffer. The smc_spd_priv pointer itself was not handled, so after tee() both the original and the cloned pipe_buffer share the same smc_spd_priv *.

When both pipes are subsequently released, smc_rx_pipe_buf_release() is called twice against the same object:

1st call: kfree(priv) sock_put(sk) smc_rx_update_cons() [correct] 2nd call: kfree(priv) sock_put(sk) smc_rx_update_cons() [UAF]

KASAN reports a slab-use-after-free in smc_rx_pipe_buf_release(), which then escalates to a NULL-pointer dereference and kernel panic via smc_rx_update_consumer() when it chases the freed priv->smc pointer:

BUG: KASAN: slab-use-after-free in smc_rx_pipe_buf_release+0x78/0x2a0 Read of size 8 at addr ffff888004a45740 by task smc_splice_tee_/74 Call Trace: <TASK> dump_stack_lvl+0x53/0x70 print_report+0xce/0x650 kasan_report+0xc6/0x100 smc_rx_pipe_buf_release+0x78/0x2a0 free_pipe_info+0xd4/0x130 pipe_release+0x142/0x160 __fput+0x1c6/0x490 __x64_sys_close+0x4f/0x90 do_syscall_64+0xa6/0x1a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK>

BUG: kernel NULL pointer dereference, address: 0000000000000020 RIP: 0010:smc_rx_update_consumer+0x8d/0x350 Call Trace: <TASK> smc_rx_pipe_buf_release+0x121/0x2a0 free_pipe_info+0xd4/0x130 pipe_release+0x142/0x160 __fput+0x1c6/0x490 __x64_sys_close+0x4f/0x90 do_syscall_64+0xa6/0x1a0 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> Kernel panic - not syncing: Fatal exception

Beyond the memory-safety problem, duplicating an SMC splice buffer is semantically questionable: smc_rx_update_cons() would advance the consumer cursor twice for the same data, corrupting receive-window accounting. A refcount on smc_spd_priv could fix the double-free, but the cursor-accounting issue would still need to be addressed separately.

The .get callback is invoked by both tee(2) and splice_pipe_to_pipe() for partial transfers; both will now return -EFAULT. Users who need to duplicate SMC socket data must use a copy-based read path.

Affected

• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 7e8916f46c2f48607f907fd401590093753a6bc5
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < ae5575e660410c8d2c5d38fb28a0f37aea945676
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 98ba5cb274768146e25ffbfde47753652c1c20d3
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 81acbd345d405994875d419d43b319fee0b9ad62
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 7bcb974c771c863e8588cea0012ac204443a7126
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 54c87a730157868543ebdfa0ecb21b4590ed23a5
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 3cc76380fea749280c026f410af56a28aaac388a
• Linux >= 9014db202cb764b8e14c53e7bacc81f9a1a2ba7f < 24dd586bb4cbba1889a50abe74143817a095c1c9
• Linux 4.18

Remediation

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