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Tue, 26 May 2026 15:24:44 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 26 May 2026 18:24:44 -0400 Message-Id: From: "Emil Tsalapatis" To: "Dawei Feng" , Cc: , , , , , , , , , , , , , , , "Zilin Guan" Subject: Re: [PATCH 2/2] bpf: cgroup: Use kvfree instead of kfree in __cgroup_bpf_run_filter_sysctl X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260526131035.1312864-1-dawei.feng@seu.edu.cn> <20260526131035.1312864-3-dawei.feng@seu.edu.cn> In-Reply-To: <20260526131035.1312864-3-dawei.feng@seu.edu.cn> On Tue May 26, 2026 at 9:10 AM EDT, Dawei Feng wrote: > proc_sys_call_handler() allocates its temporary sysctl buffer with > kvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since > kvzalloc() may fall back to vmalloc() for large allocations, freeing > that buffer with kfree() is wrong and can corrupt memory. > > Use kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc > allocations. > > The bug was first flagged by an experimental analysis tool we are > developing for kernel memory-management bugs while analyzing > v6.13-rc1. The tool is still under development and is not yet publicly > available. Manual inspection confirms that the bug is still > present in v7.1-rc5. > > Reproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with > KASAN and CONFIG_FAILSLAB enabled. The reproducer confines failslab > injections to the proc_sys_call_handler() range, uses > stacktrace-depth=3D32, and injects fail-nth=3D1 while writing 8191 bytes = to > /proc/sys/kernel/domainname from a task in the target cgroup. On the > patch1-only kernel, fail-nth=3D1 triggered the fault: > > BUG: unable to handle page fault for address: ffffeb0200024d48 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: Oops: 0000 SMP KASAN NOPTI > CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-0068= 6-g97625979a5d4 PREEMPT(lazy) > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01= /2014 > RIP: 0010:kfree+0x6e/0x510 > Code: 80 48 01 ef 0f 82 ae 04 00 00 48 c7 c0 00 00 00 80 48 2b 05 04 1b= 23 04 48 01 c7 48 c1 ef 0c 48 c1 e7 06 48 03 3d e2 1a 23 04 <4c> 8b 57 08 = 4c 89 d0 83 e0 01 48 83 e8 01 49 09 c2 49 > > RSP: 0018:ffff888108de7ab8 EFLAGS: 00010282 > RAX: 0000777f80000000 RBX: ffff88815af398c0 RCX: 0000000000000080 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffeb0200024d40 > RBP: ffffc90000935000 R08: 0000000000000001 R09: 0000000000000001 > R10: ffffffff86b4b297 R11: 0000000000000000 R12: ffffffff819b71fd > R13: 0000000000000001 R14: ffff888108de7cc0 R15: 0000000000000000 > FS: 00007f8988cc2b80(0000) GS:ffff8881d3256000(0000) knlGS:00000000000= 00000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: ffffeb0200024d48 CR3: 0000000101d6b000 CR4: 0000000000350ef0 > Call Trace: > > ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30 > __cgroup_bpf_run_filter_sysctl+0x74d/0xc30 > ? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10 > ? srso_return_thunk+0x5/0x5f > ? __kvmalloc_node_noprof+0x345/0x870 > ? proc_sys_call_handler+0x250/0x480 > ? srso_return_thunk+0x5/0x5f > proc_sys_call_handler+0x3a2/0x480 > ? __pfx_proc_sys_call_handler+0x10/0x10 > ? srso_return_thunk+0x5/0x5f > ? selinux_file_permission+0x39f/0x500 > ? srso_return_thunk+0x5/0x5f > ? lock_is_held_type+0x9e/0x120 > vfs_write+0x98e/0x1000 > ? srso_return_thunk+0x5/0x5f > ? kmem_cache_free+0x308/0x550 > ? __pfx_vfs_write+0x10/0x10 > ? __pfx_do_sys_openat2+0x10/0x10 > ksys_write+0xf2/0x1d0 > ? __pfx_ksys_write+0x10/0x10 > ? srso_return_thunk+0x5/0x5f > ? trace_irq_enable.constprop.0+0x110/0x140 > do_syscall_64+0x115/0x690 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f8988dd8907 > Code: 10 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1= e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f= 0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 > > RSP: 002b:00007fff4069b878 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f8988dd8907 > RDX: 0000000000001fff RSI: 0000564f97ef46b0 RDI: 0000000000000005 > RBP: 0000564f97ef46b0 R08: 0000000000000000 R09: 0000564f97ef46b0 > R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000000 > R13: 0000000000001fff R14: 0000000000000005 R15: 0000000000000001 > > With this fix applied, rerunning the reproducer with the same > fail-nth=3D1 setup yields no corresponding Oops reports. > > Fixes: 4508943794ef ("proc: use kvzalloc for our kernel buffer") > Cc: stable@vger.kernel.org > > Signed-off-by: Zilin Guan > Signed-off-by: Dawei Feng > --- Reviewed-by: Emil Tsalapatis > kernel/bpf/cgroup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c > index 8715a014c21d..f4eefdacd453 100644 > --- a/kernel/bpf/cgroup.c > +++ b/kernel/bpf/cgroup.c > @@ -1936,7 +1936,7 @@ int __cgroup_bpf_run_filter_sysctl(struct ctl_table= _header *head, > kfree(ctx.cur_val); > =20 > if (!ret && ctx.new_updated) { > - kfree(*buf); > + kvfree(*buf); > *buf =3D ctx.new_val; > *pcount =3D ctx.new_len; > } else {