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

tracing/hist: Fix out-of-bound write on action_data.var_ref_idx

When generate a synthetic event with many params and then create a trace action for it [1], kernel panic happened [2].

It is because that in trace_action_create() data->n_params is up to SYNTH_FIELDS_MAX (current value is 64), and array data->var_ref_idx keeps indices into array hist_data->var_refs for each synthetic event param, but the length of data->var_ref_idx is TRACING_MAP_VARS_MAX (current value is 16), so out-of-bound write happened when data->n_params more than 16. In this case, data->match_data.event is overwritten and eventually cause the panic.

To solve the issue, adjust the length of data->var_ref_idx to be SYNTH_FIELDS_MAX and add sanity checks to avoid out-of-bound write.

[1]

cd /sys/kernel/tracing/

echo my_synth_event int v1; int v2; int v3; int v4; int v5; int v6;

int v7; int v8; int v9; int v10; int v11; int v12; int v13; int v14; int v15; int v16; int v17; int v18; int v19; int v20; int v21; int v22; int v23; int v24; int v25; int v26; int v27; int v28; int v29; int v30; int v31; int v32; int v33; int v34; int v35; int v36; int v37; int v38; int v39; int v40; int v41; int v42; int v43; int v44; int v45; int v46; int v47; int v48; int v49; int v50; int v51; int v52; int v53; int v54; int v55; int v56; int v57; int v58; int v59; int v60; int v61; int v62; int v63 » synthetic_events

echo hist:keys=pid:ts0=common_timestamp.usecs if comm==bash »

events/sched/sched_waking/trigger

echo hist:keys=next_pid:onmatch(sched.sched_waking).my_synth_event(

pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid, pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid, pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid,pid, pid,pid,pid,pid,pid,pid,pid,pid,pid) » events/sched/sched_switch/trigger

[2] BUG: unable to handle page fault for address: ffff91c900000000 PGD 61001067 P4D 61001067 PUD 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 2 PID: 322 Comm: bash Tainted: G W 6.1.0-rc8+ #229 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 RIP: 0010:strcmp+0xc/0x30 Code: 75 f7 31 d2 44 0f b6 04 16 44 88 04 11 48 83 c2 01 45 84 c0 75 ee c3 cc cc cc cc 0f 1f 00 31 c0 eb 08 48 83 c0 01 84 d2 74 13 <0f> b6 14 07 3a 14 06 74 ef 19 c0 83 c8 01 c3 cc cc cc cc 31 c3 RSP: 0018:ffff9b3b00f53c48 EFLAGS: 00000246 RAX: 0000000000000000 RBX: ffffffffba958a68 RCX: 0000000000000000 RDX: 0000000000000010 RSI: ffff91c943d33a90 RDI: ffff91c900000000 RBP: ffff91c900000000 R08: 00000018d604b529 R09: 0000000000000000 R10: ffff91c9483eddb1 R11: ffff91ca483eddab R12: ffff91c946171580 R13: ffff91c9479f0538 R14: ffff91c9457c2848 R15: ffff91c9479f0538 FS: 00007f1d1cfbe740(0000) GS:ffff91c9bdc80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff91c900000000 CR3: 0000000006316000 CR4: 00000000000006e0 Call Trace: __find_event_file+0x55/0x90 action_create+0x76c/0x1060 event_hist_trigger_parse+0x146d/0x2060 ? event_trigger_write+0x31/0xd0 trigger_process_regex+0xbb/0x110 event_trigger_write+0x6b/0xd0 vfs_write+0xc8/0x3e0 ? alloc_fd+0xc0/0x160 ? preempt_count_add+0x4d/0xa0 ? preempt_count_add+0x70/0xa0 ksys_write+0x5f/0xe0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f1d1d0cf077 Code: 64 89 02 48 c7 c0 ff ff ff ff eb bb 0f 1f 80 00 00 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 RSP: 002b:00007ffcebb0e568 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 0000000000000143 RCX: 00007f1d1d0cf077 RDX: 0000000000000143 RSI: 00005639265aa7e0 RDI: 0000000000000001 RBP: 00005639265aa7e0 R08: 000000000000000a R09: 0000000000000142 R —truncated—

Weakness

The product writes data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

• Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

• Consider adhering to the following rules when allocating and managing an application’s memory:

• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

References

• https://git.kernel.org/stable/c/04241956ce8825ff06e06e4083e7b692e9d5f712
• https://git.kernel.org/stable/c/0cb31bd88361edb96cfc622648717ba348f0f4dc
• https://git.kernel.org/stable/c/15697f653399253f9be4ed2a1e03d795f3cfee94
• https://git.kernel.org/stable/c/82470f7d9044842618c847a7166de2b7458157a7
• https://git.kernel.org/stable/c/b4efdc219fb8cfa066c7042e636ab8ad6d7e7494
• https://git.kernel.org/stable/c/cf79d5410a569dad1d4112b5c3c02383cca8213a