[SRU][J/N/O/P][PATCH v2 0/1] iBFT iSCSI out-of-bounds shift UBSAN warning

[Chengen Du]

BugLink: https://bugs.launchpad.net/bugs/2097824

SRU Justification:

[Impact]
During an iSCSI boot in an IPv6 environment, `iscsistart` continues to access the `/sys/firmware/ibft/ethernetX/subnet-mask` entry, despite subnet masks being irrelevant for IPv6. Since the IPv6 prefix length is 64, this leads to a negative shift exponent, triggering a UBSAN warning.

[Fix]
A commit has been made to fix this issue.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=07e0d99a2f701123ad3104c0f1a1e66bce74d6e5

[Test Plan]
1. Set up a machine with an iSCSI backend in an IPv6-only environment.
2. Power on the machine and verify that the following error does not occur:
[ 105.283243] UBSAN: shift-out-of-bounds in /build/linux-oracle-cD7q0d/linux-oracle-6.8.0/drivers/firmware/iscsi_ibft.c:313:9
[ 105.432609] shift exponent -32 is negative
[ 105.498209] CPU: 106 PID: 2536 Comm: iscsistart Not tainted 6.8.0-1008-oracle #8-Ubuntu
[ 105.610611] Hardware name: Oracle Corporation ORACLE SERVER E4-2c/Asm,MB Tray,2U,E4-2c, BIOS 78016100 04/11/2024
[ 105.749047] Call Trace:
[ 105.794939] <TASK>
[ 105.832503] dump_stack_lvl+0x76/0xa0
[ 105.876679] dump_stack+0x10/0x20
[ 105.916742] __ubsan_handle_shift_out_of_bounds+0x199/0x370
[ 105.983788] ibft_attr_show_nic.cold+0x17/0x2c [iscsi_ibft]
[ 106.050817] iscsi_boot_show_attribute+0x3f/0x70 [iscsi_boot_sysfs]
[ 106.126167] sysfs_kf_seq_show+0xa7/0x120
[ 106.174475] kernfs_seq_show+0x27/0x40
[ 106.219654] seq_read_iter+0x132/0x4b0
[ 106.264824] kernfs_fop_read_iter+0x34/0x40
[ 106.315190] vfs_read+0x258/0x390
[ 106.355160] ksys_read+0x73/0x100
[ 106.395116] __x64_sys_read+0x19/0x30
[ 106.439234] x64_sys_call+0x1ada/0x25c0
[ 106.485422] do_syscall_64+0x7f/0x180
[ 106.529528] ? srso_alias_return_thunk+0x5/0xfbef5
[ 106.587154] ? syscall_exit_to_user_mode+0x89/0x260
[ 106.645810] ? srso_alias_return_thunk+0x5/0xfbef5
[ 106.703424] ? do_syscall_64+0x8c/0x180
[ 106.749594] ? srso_alias_return_thunk+0x5/0xfbef5
[ 106.807197] ? __do_sys_newfstatat+0x44/0x90
[ 106.858552] ? srso_alias_return_thunk+0x5/0xfbef5
[ 106.916147] ? syscall_exit_to_user_mode+0x89/0x260
[ 106.974771] ? srso_alias_return_thunk+0x5/0xfbef5
[ 107.032350] ? do_syscall_64+0x8c/0x180
[ 107.078488] ? do_syscall_64+0x8c/0x180
[ 107.124620] ? exc_page_fault+0x94/0x190
[ 107.171789] entry_SYSCALL_64_after_hwframe+0x78/0x80
[ 107.232475] RIP: 0033:0x764465a69a61
[ 107.275484] Code: 00 48 8b 15 b9 73 0e 00 f7 d8 64 89 02 b8 ff ff ff ff eb bd e8 40 c4 01 00 f3 0f 1e fa 80 3d e5 f5 0e 00 00 74 13 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 4f c3 66 0f 1f 44 00 00 55 48 89 e5 48 83 ec
[ 107.500766] RSP: 002b:00007ffc83fa6798 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 107.591622] RAX: ffffffffffffffda RBX: 00007ffc83fa6840 RCX: 0000764465a69a61
[ 107.677276] RDX: 0000000000000100 RSI: 00007ffc83fa6840 RDI: 0000000000000003
[ 107.762929] RBP: 00007ffc83fa6f80 R08: 00005d0f5c8b7fb4 R09: 0000000000000007
[ 107.848624] R10: 0000000000000000 R11: 0000000000000246 R12: 00005d0f5c8b7fb4
[ 107.934283] R13: 00007ffc83fa6940 R14: 00005d0f5c8bf650 R15: 0000000000000003
[ 108.019949] </TASK>

[Where problems could occur]
The patch resolves the UBSAN warning that occurs when accessing the `/sys/firmware/ibft/ethernetX/subnet-mask` entry. However, if any regressions occur, the entry may display an incorrect value.

V1 -> V2: No backport to Focal is needed, as `CONFIG_UBSAN` is not enabled.

Chengen Du (1):
  iscsi_ibft: Fix UBSAN shift-out-of-bounds warning in
    ibft_attr_show_nic()

 drivers/firmware/iscsi_ibft.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

-- 
2.43.0