On Wed, Dec 15, 2021 at 11:20 AM Scott Mayhew <smayhew@xxxxxxxxxx> wrote:
>
> selinux_sb_mnt_opts_compat() is called via sget_fc() under the sb_lock
> spinlock, so it can't use GFP_KERNEL allocations:
>
> [ 868.565200] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:230
> [ 868.568246] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 4914, name: mount.nfs
> [ 868.569626] preempt_count: 1, expected: 0
> [ 868.570215] RCU nest depth: 0, expected: 0
> [ 868.570809] Preemption disabled at:
> [ 868.570810] [<0000000000000000>] 0x0
> [ 868.571848] CPU: 1 PID: 4914 Comm: mount.nfs Kdump: loaded Tainted: G W 5.16.0-rc5.2585cf9dfa #1
> [ 868.573273] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-4.fc34 04/01/2014
> [ 868.574478] Call Trace:
> [ 868.574844] <TASK>
> [ 868.575156] dump_stack_lvl+0x34/0x44
> [ 868.575692] __might_resched.cold+0xd6/0x10f
> [ 868.576308] slab_pre_alloc_hook.constprop.0+0x89/0xf0
> [ 868.577046] __kmalloc_track_caller+0x72/0x420
> [ 868.577684] ? security_context_to_sid_core+0x48/0x2b0
> [ 868.578569] kmemdup_nul+0x22/0x50
> [ 868.579108] security_context_to_sid_core+0x48/0x2b0
> [ 868.579854] ? _nfs4_proc_pathconf+0xff/0x110 [nfsv4]
> [ 868.580742] ? nfs_reconfigure+0x80/0x80 [nfs]
> [ 868.581355] security_context_str_to_sid+0x36/0x40
> [ 868.581960] selinux_sb_mnt_opts_compat+0xb5/0x1e0
> [ 868.582550] ? nfs_reconfigure+0x80/0x80 [nfs]
> [ 868.583098] security_sb_mnt_opts_compat+0x2a/0x40
> [ 868.583676] nfs_compare_super+0x113/0x220 [nfs]
> [ 868.584249] ? nfs_try_mount_request+0x210/0x210 [nfs]
> [ 868.584879] sget_fc+0xb5/0x2f0
> [ 868.585267] nfs_get_tree_common+0x91/0x4a0 [nfs]
> [ 868.585834] vfs_get_tree+0x25/0xb0
> [ 868.586241] fc_mount+0xe/0x30
> [ 868.586605] do_nfs4_mount+0x130/0x380 [nfsv4]
> [ 868.587160] nfs4_try_get_tree+0x47/0xb0 [nfsv4]
> [ 868.587724] vfs_get_tree+0x25/0xb0
> [ 868.588193] do_new_mount+0x176/0x310
> [ 868.588782] __x64_sys_mount+0x103/0x140
> [ 868.589388] do_syscall_64+0x3b/0x90
> [ 868.589935] entry_SYSCALL_64_after_hwframe+0x44/0xae
> [ 868.590699] RIP: 0033:0x7f2b371c6c4e
> [ 868.591239] Code: 48 8b 0d dd 71 0e 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d aa 71 0e 00 f7 d8 64 89 01 48
> [ 868.593810] RSP: 002b:00007ffc83775d88 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> [ 868.594691] RAX: ffffffffffffffda RBX: 00007ffc83775f10 RCX: 00007f2b371c6c4e
> [ 868.595504] RDX: 0000555d517247a0 RSI: 0000555d51724700 RDI: 0000555d51724540
> [ 868.596317] RBP: 00007ffc83775f10 R08: 0000555d51726890 R09: 0000555d51726890
> [ 868.597162] R10: 0000000000000000 R11: 0000000000000246 R12: 0000555d51726890
> [ 868.598005] R13: 0000000000000003 R14: 0000555d517246e0 R15: 0000555d511ac925
> [ 868.598826] </TASK>
>
> Fixes: 69c4a42d72eb ("lsm,selinux: add new hook to compare new mount to an existing mount")
> Signed-off-by: Scott Mayhew <smayhew@xxxxxxxxxx>
> ---
> security/selinux/hooks.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 62d30c0a30c2..534e8a4747f8 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -611,10 +611,11 @@ static int bad_option(struct superblock_security_struct *sbsec, char flag,
> return 0;
> }
>
> -static int parse_sid(struct super_block *sb, const char *s, u32 *sid)
> +static int __parse_sid(struct super_block *sb, const char *s, u32 *sid,
> + gfp_t gfp)
> {
> int rc = security_context_str_to_sid(&selinux_state, s,
> - sid, GFP_KERNEL);
> + sid, gfp);
> if (rc)
> pr_warn("SELinux: security_context_str_to_sid"
> "(%s) failed for (dev %s, type %s) errno=%d\n",
> @@ -622,6 +623,11 @@ static int parse_sid(struct super_block *sb, const char *s, u32 *sid)
> return rc;
> }
>
> +static int parse_sid(struct super_block *sb, const char *s, u32 *sid)
> +{
> + return __parse_sid(sb, s, sid, GFP_KERNEL);
> +}
Thanks for both reporting the problem and supplying a patch to fix it!
I think I would prefer to see parse_sid() updated to take a gfp
parameter and skip the __parse_sid()/parse_sid() wrapper. Yes, the
patch will be a bit more intrusive with all of the caller updates, but
we only have to backport up to v5.13 and the resulting code will be
cleaner moving forward.
--
paul moore
www.paul-moore.com
