A ceph user has reported that ceph is crashing with kernel NULL pointer
dereference. Following is the backtrace.
/proc/version: Linux version 5.16.2-arch1-1 (linux@archlinux) (gcc (GCC)
11.1.0, GNU ld (GNU Binutils) 2.36.1) #1 SMP PREEMPT Thu, 20 Jan 2022
16:18:29 +0000
distro / arch: Arch Linux / x86_64
SELinux is not enabled
ceph cluster version: 16.2.7 (
dd0603118f56ab514f133c8d2e3adfc983942503)
relevant dmesg output:
[ 30.947129] BUG: kernel NULL pointer dereference, address:
0000000000000000
[ 30.947206] #PF: supervisor read access in kernel mode
[ 30.947258] #PF: error_code(0x0000) - not-present page
[ 30.947310] PGD 0 P4D 0
[ 30.947342] Oops: 0000 [#1] PREEMPT SMP PTI
[ 30.947388] CPU: 5 PID: 778 Comm: touch Not tainted 5.16.2-arch1-1 #1
86fbf2c313cc37a553d65deb81d98e9dcc2a3659
[ 30.947486] Hardware name: Gigabyte Technology Co., Ltd. B365M
DS3H/B365M DS3H, BIOS F5 08/13/2019
[ 30.947569] RIP: 0010:strlen+0x0/0x20
[ 30.947616] Code: b6 07 38 d0 74 16 48 83 c7 01 84 c0 74 05 48 39 f7 75
ec 31 c0 31 d2 89 d6 89 d7 c3 48 89 f8 31 d2 89 d6 89 d7 c3 0
f 1f 40 00 <80> 3f 00 74 12 48 89 f8 48 83 c0 01 80 38 00 75 f7 48 29 f8 31
ff
[ 30.947782] RSP: 0018:
ffffa4ed80ffbbb8 EFLAGS:
00010246
[ 30.947836] RAX:
0000000000000000 RBX:
ffffa4ed80ffbc60 RCX:
0000000000000000
[ 30.947904] RDX:
0000000000000000 RSI:
0000000000000000 RDI:
0000000000000000
[ 30.947971] RBP:
ffff94b0d15c0ae0 R08:
0000000000000000 R09:
0000000000000000
[ 30.948040] R10:
0000000000000000 R11:
0000000000000000 R12:
0000000000000000
[ 30.948106] R13:
0000000000000001 R14:
ffffa4ed80ffbc60 R15:
0000000000000000
[ 30.948174] FS:
00007fc7520f0740(0000) GS:
ffff94b7ced40000(0000)
knlGS:
0000000000000000
[ 30.948252] CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
[ 30.948308] CR2:
0000000000000000 CR3:
0000000104a40001 CR4:
00000000003706e0
[ 30.948376] Call Trace:
[ 30.948404] <TASK>
[ 30.948431] ceph_security_init_secctx+0x7b/0x240 [ceph
49f9c4b9bf5be8760f19f1747e26da33920bce4b]
[ 30.948582] ceph_atomic_open+0x51e/0x8a0 [ceph
49f9c4b9bf5be8760f19f1747e26da33920bce4b]
[ 30.948708] ? get_cached_acl+0x4d/0xa0
[ 30.948759] path_openat+0x60d/0x1030
[ 30.948809] do_filp_open+0xa5/0x150
[ 30.948859] do_sys_openat2+0xc4/0x190
[ 30.948904] __x64_sys_openat+0x53/0xa0
[ 30.948948] do_syscall_64+0x5c/0x90
[ 30.948989] ? exc_page_fault+0x72/0x180
[ 30.949034] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 30.949091] RIP: 0033:0x7fc7521e25bb
[ 30.950849] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00
00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 0
0 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 54 24 28 64 48 2b 14
25
Core of the problem is that ceph checks for return code from
security_dentry_init_security() and if return code is 0, it assumes
everything is fine and continues to call strlen(name), which crashes.
Typically SELinux LSM returns 0 and sets name to "security.selinux" and
it is not a problem. Or if selinux is not compiled in or disabled, it
returns -EOPNOTSUP and ceph deals with it.
But somehow in this configuration, 0 is being returned and "name" is
not being initialized and that's creating the problem.
Our suspicion is that BPF LSM is registering a hook for
dentry_init_security() and returns hook default of 0.
LSM_HOOK(int, 0, dentry_init_security, struct dentry *dentry,...)
I have not been able to reproduce it just by doing CONFIG_BPF_LSM=y.
Stephen has tested the patch though and confirms it solves the problem
for him.
dentry_init_security() is written in such a way that it expects only one
LSM to register the hook. Atleast that's the expectation with current code.
If another LSM returns a hook and returns default, it will simply return
0 as of now and that will break ceph.
Hence, suggestion is that change semantics of this hook a bit. If there
are no LSMs or no LSM is taking ownership and initializing security context,
then return -EOPNOTSUP. Also allow at max one LSM to initialize security
context. This hook can't deal with multiple LSMs trying to init security
context. This patch implements this new behavior.
Reported-by: Stephen Muth <smuth4@gmail.com>
Tested-by: Stephen Muth <smuth4@gmail.com>
Suggested-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: <stable@vger.kernel.org> # 5.16.0
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: James Morris <jmorris@namei.org>
int len, void **mnt_opts)
LSM_HOOK(int, 0, move_mount, const struct path *from_path,
const struct path *to_path)
-LSM_HOOK(int, 0, dentry_init_security, struct dentry *dentry,
+LSM_HOOK(int, -EOPNOTSUPP, dentry_init_security, struct dentry *dentry,
int mode, const struct qstr *name, const char **xattr_name,
void **ctx, u32 *ctxlen)
LSM_HOOK(int, 0, dentry_create_files_as, struct dentry *dentry, int mode,
const char **xattr_name, void **ctx,
u32 *ctxlen)
{
- return call_int_hook(dentry_init_security, -EOPNOTSUPP, dentry, mode,
- name, xattr_name, ctx, ctxlen);
+ struct security_hook_list *hp;
+ int rc;
+
+ /*
+ * Only one module will provide a security context.
+ */
+ hlist_for_each_entry(hp, &security_hook_heads.dentry_init_security, list) {
+ rc = hp->hook.dentry_init_security(dentry, mode, name,
+ xattr_name, ctx, ctxlen);
+ if (rc != LSM_RET_DEFAULT(dentry_init_security))
+ return rc;
+ }
+ return LSM_RET_DEFAULT(dentry_init_security);
}
EXPORT_SYMBOL(security_dentry_init_security);
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