[PATCH v2] mm/kmemleak: Fix sleeping function called from invalid context at print message

Alessandro Carminati
2024-12-17T14:21:45Z

Address a bug in the kernel that triggers a "sleeping function called from
invalid context" warning when /sys/kernel/debug/kmemleak is printed under
specific conditions:
- CONFIG_PREEMPT_RT=y
- Set SELinux as the LSM for the system
- Set kptr_restrict to 1
- kmemleak buffer contains at least one item

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 136, name: cat
preempt_count: 1, expected: 0
RCU nest depth: 2, expected: 2
6 locks held by cat/136:
#0: ffff32e64bcbf950 (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0xb8/0xe30
#1: ffffafe6aaa9dea0 (scan_mutex){+.+.}-{3:3}, at: kmemleak_seq_start+0x34/0x128
#3: ffff32e6546b1cd0 (&object->lock){....}-{2:2}, at: kmemleak_seq_show+0x3c/0x1e0
#4: ffffafe6aa8d8560 (rcu_read_lock){....}-{1:2}, at: has_ns_capability_noaudit+0x8/0x1b0
#5: ffffafe6aabbc0f8 (notif_lock){+.+.}-{2:2}, at: avc_compute_av+0xc4/0x3d0
irq event stamp: 136660
hardirqs last enabled at (136659): [<ffffafe6a80fd7a0>] _raw_spin_unlock_irqrestore+0xa8/0xd8
hardirqs last disabled at (136660): [<ffffafe6a80fd85c>] _raw_spin_lock_irqsave+0x8c/0xb0
softirqs last enabled at (0): [<ffffafe6a5d50b28>] copy_process+0x11d8/0x3df8
softirqs last disabled at (0): [<0000000000000000>] 0x0
Preemption disabled at:
[<ffffafe6a6598a4c>] kmemleak_seq_show+0x3c/0x1e0
CPU: 1 UID: 0 PID: 136 Comm: cat Tainted: G E 6.11.0-rt7+ #34
Tainted: [E]=UNSIGNED_MODULE
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0xa0/0x128
show_stack+0x1c/0x30
dump_stack_lvl+0xe8/0x198
dump_stack+0x18/0x20
rt_spin_lock+0x8c/0x1a8
avc_perm_nonode+0xa0/0x150
cred_has_capability.isra.0+0x118/0x218
selinux_capable+0x50/0x80
security_capable+0x7c/0xd0
has_ns_capability_noaudit+0x94/0x1b0
has_capability_noaudit+0x20/0x30
restricted_pointer+0x21c/0x4b0
pointer+0x298/0x760
vsnprintf+0x330/0xf70
seq_printf+0x178/0x218
print_unreferenced+0x1a4/0x2d0
kmemleak_seq_show+0xd0/0x1e0
seq_read_iter+0x354/0xe30
seq_read+0x250/0x378
full_proxy_read+0xd8/0x148
vfs_read+0x190/0x918
ksys_read+0xf0/0x1e0
__arm64_sys_read+0x70/0xa8
invoke_syscall.constprop.0+0xd4/0x1d8
el0_svc+0x50/0x158
el0t_64_sync+0x17c/0x180

%pS and %pK, in the same back trace line, are redundant, and %pS can void
%pK service in certain contexts.

%pS alone already provides the necessary information, and if it cannot
resolve the symbol, it falls back to printing the raw address voiding
the original intent behind the %pK.

Additionally, %pK requires a privilege check CAP_SYSLOG enforced through
the LSM, which can trigger a "sleeping function called from invalid
context" warning under RT_PREEMPT kernels when the check occurs in an
atomic context. This issue may also affect other LSMs.

This change avoids the unnecessary privilege check and resolves the
sleeping function warning without any loss of information.

Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
---
mm/kmemleak.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 2a945c07ae99..737af23f4f4e 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -373,7 +373,7 @@ static void print_unreferenced(struct seq_file *seq,

for (i = 0; i < nr_entries; i++) {
void *ptr = (void *)entries[i];
- warn_or_seq_printf(seq, " [<%pK>] %pS\n", ptr, ptr);
+ warn_or_seq_printf(seq, " %pS\n", ptr);
}
}

--
2.34.1