Re: [PATCH v2] selinux: use GFP_ATOMIC in convert_context()

From: Ondrej Mosnacek
Date: Wed Oct 19 2022 - 10:22:43 EST


On Wed, Oct 19, 2022 at 4:56 AM GONG, Ruiqi <gongruiqi1@xxxxxxxxxx> wrote:
>
> The following warning was triggered on a hardware environment:
>
> SELinux: Converting 162 SID table entries...
> BUG: sleeping function called from invalid context at __might_sleep+0x60/0x74 0x0
> in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 5943, name: tar
> CPU: 7 PID: 5943 Comm: tar Tainted: P O 5.10.0 #1
> Call trace:
> dump_backtrace+0x0/0x1c8
> show_stack+0x18/0x28
> dump_stack+0xe8/0x15c
> ___might_sleep+0x168/0x17c
> __might_sleep+0x60/0x74
> __kmalloc_track_caller+0xa0/0x7dc
> kstrdup+0x54/0xac
> convert_context+0x48/0x2e4
> sidtab_context_to_sid+0x1c4/0x36c
> security_context_to_sid_core+0x168/0x238
> security_context_to_sid_default+0x14/0x24
> inode_doinit_use_xattr+0x164/0x1e4
> inode_doinit_with_dentry+0x1c0/0x488
> selinux_d_instantiate+0x20/0x34
> security_d_instantiate+0x70/0xbc
> d_splice_alias+0x4c/0x3c0
> ext4_lookup+0x1d8/0x200 [ext4]
> __lookup_slow+0x12c/0x1e4
> walk_component+0x100/0x200
> path_lookupat+0x88/0x118
> filename_lookup+0x98/0x130
> user_path_at_empty+0x48/0x60
> vfs_statx+0x84/0x140
> vfs_fstatat+0x20/0x30
> __se_sys_newfstatat+0x30/0x74
> __arm64_sys_newfstatat+0x1c/0x2c
> el0_svc_common.constprop.0+0x100/0x184
> do_el0_svc+0x1c/0x2c
> el0_svc+0x20/0x34
> el0_sync_handler+0x80/0x17c
> el0_sync+0x13c/0x140
> SELinux: Context system_u:object_r:pssp_rsyslog_log_t:s0:c0 is not valid (left unmapped).
>
> It was found that within a critical section of spin_lock_irqsave in
> sidtab_context_to_sid(), convert_context() (hooked by
> sidtab_convert_params.func) might cause the process to sleep via
> allocating memory with GFP_KERNEL, which is problematic.
>
> As Ondrej pointed out [1], convert_context()/sidtab_convert_params.func
> has another caller sidtab_convert_tree(), which is okay with GFP_KERNEL.
> Therefore, fix this problem by adding a gfp_t argument for
> convert_context()/sidtab_convert_params.func and pass GFP_KERNEL/_ATOMIC
> properly in individual callers.
>
> Link: https://lore.kernel.org/all/20221018120111.1474581-1-gongruiqi1@xxxxxxxxxx/ [1]
> Reported-by: Tan Ninghao <tanninghao1@xxxxxxxxxx>
> Fixes: ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve performance")
> Signed-off-by: GONG, Ruiqi <gongruiqi1@xxxxxxxxxx>
> ---
>
> v2: change as Ondrej suggests & redraft commit message

This looks good, thanks!

Reviewed-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>

> [...]

--
Ondrej Mosnacek
Senior Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.